1. Field of Invention
The present invention relates generally to the mechanical and electrical arts. In particular, the invention relates to systems and methods for detecting fluid flow and for anticipating demands for fluid flow.
2. Description of Related Art
Modern plumbing systems typically provide both hot water and cold water to various locations in a house or other structure. Water at these locations can be used for many purposes, for example washing, bathing, laundry, drinking and cooking. Each location where water is used has an outlet controlled by valves, also sometimes known as faucets, taps, or spigots. A valve can control the flow or mix hot and cold water to the outlet. Hot and cold water are supplied to the outlet location by plumbing systems consisting of various types of pipe or plumbing lines configured into a supply network. For example, many household systems supplying potable water use copper pipe or galvanized iron pipe. Hot and cold water are typically supplied by separate pipes. “Cold” water is actually water supplied at ambient temperature, near the temperature received from the water supply, well, or utility. “Hot” water is obtained by routing water from the utility, supply or well to a heating device before sending to the hot water plumbing lines.
A problem arises where a hot water outlet is remote from the water heating device because a volume of water at a temperature lower than that provided by the water heating device exists in the interconnecting pipes.
During periods when hot water is not flowing in a hot water pipe, the temperature of the stagnant water in the pipe approaches ambient temperature. A user opening a remote outlet such as a valve or faucet must therefore wait for the relatively cool water in the pipe to be purged before hot water reaches the outlet. In conventional systems, the purged relatively cold water is allowed to flow down the drain and is therefore wasted.
Thus conventional systems not only waste water, but they require a user to wait until relatively cold water in the pipe or line is purged. These problems are aggravated in cooler ambient temperatures or in larger homes or buildings with correspondingly larger volumes of water stored in their respective water plumbing systems.
Insulating the hot water lines is a solution known in the art. This solution slows the cooling of the water in the hot water lines; however, the water cools eventually and the problems of delay and waste remain.
Recirculating solutions are also known in the art. Here, the cooler water in a hot water line is removed to the cold water system for reuse, rather than discarded. Some recirculating systems are implemented by installing an additional plumbing line, running from the furthest point in the hot water distribution line back to the hot water heating device. Thus the hot water line and recirculation return line form a complete circuit through the hot water heating device.
In a typical recirculation system, a recirculation pump draws the cooler water from the hot water supply lines and moves it into the hot water heating device, simultaneously drawing hot water into the hot water supply line. This fills the hot water supply system rapidly with hot water. The effect is to provide hot water to an outlet much more quickly when the pump is running, and to avoid wasting water.
However, a difficulty arises in trying to determine when to activate the recirculation pump. Running the pump continuously is highly inefficient because the entire hot water plumbing system is continuously replenished with hot water, continuously remains hot and continuously transfers heat to the surroundings even when hot water is not needed by users. In many hot water systems, the periods of use are intermittent and shorter than periods of non-usage. Continuous pump operation also consumes electricity and may contribute to wear on pipes and lead to repairs or early replacement of plumbing systems and related components. Pump life is also unnecessarily consumed by operation during periods when there is no user demand for hot water.
The United States Department of Energy has identified control of hot water recirculation systems as a challenge and inadequate control of such systems as a source of energy loss. Their website, in a summary of the Building America Expert Meeting held in July 2004 states:
Some conventional systems operate the pump intermittently, using a temperature regulation system. In this system the pump is turned on when a single temperature measured at some point in the system falls below a fixed threshold value. This type of system keeps the entire hot water circuit at an elevated temperature at all times. This scheme suffers from much the same energy wasting limitation as continuous operation, in that energy is lost from the pipes continuously. However, it does reduce the delay that occurs before hot water is delivered to an outlet.
Other known systems use a timer to operate the recirculation pump during selected periods. These timers are typically electromechanical having a limited number of user selectable on and off events during a repeating 24 hour time interval. Here, the user must anticipate when hot water will be needed and set the timer accordingly.
This scheme has several limitations including the following. First, a user must predict when hot water will be needed and set the timer accordingly. Second, setting such timers is cumbersome and error prone. Third, these timers offer only a limited number of user selectable on and off events. Fourth, these timers do not distinguish usage patters that differ with the day of the week or month. Fifth, these timers do not learn the habits of hot water users. And finally, these timers have limited resolution and accuracy.
Often hot water will be needed at a time other than when pump operation is scheduled. Such events may entirely unpredictable or they may reflect a gradual or sudden change in the user's hot water demand habits. In other cases, the user's hot water demands may simply differ based on day of the week or for holidays.
Timer systems will also activate at times when hot water is not needed, as during vacations. This uncertainty in predicting when hot water is needed leads users to set the pump to run for much longer periods than the period of actual demand. This wastes energy for water heating and for pump operation.
In addition, the timer will lose its time setting if electrical power is lost. In addition, timers do not compensate for changes in daylight savings time or sunrise and day length, all of which can affect a usage schedule and may cause the pump to operate at times when hot water is not needed, or to not operate when needed.
Some systems attempt to supply hot water only when a user desires hot water. Such manually activated demand systems require a user to request hot water by operating a switch that activates a pump. To be useful, these systems require switches located near each remote outlet.
Manually activated demand systems also suffer from various limitations. Users must be trained to activate a manual device and to open the hot water outlet valve or faucet at the appropriate time. Such devices are unfamiliar and children or guests may have difficulty obtaining hot water. Manually activated water demand switches must be located near each remote hot water outlet, often requiring extensive wiring between each device and the pump. Remote activation devices require power, supplied either by wiring connections, or by batteries that must be changed periodically. Where batteries are used, a failed battery causes the system to become inoperative and its benefit is lost.
What is needed is a simple control system that solves these problems by obtaining and analyzing temperature, time, and hot water system data to optimize the process for selecting the periods during which the pump will run.
An improved system and method for detecting and anticipating fluid demand from a pipe has been found.
In the present invention for detecting fluid demand a first pipe transports a fluid, a sensor senses a temperature varying with the temperature of the fluid, a processor in signal communication with the temperature sensor evaluates a time rate of temperature change, and a current flow in an electrical circuit is responsive to the time rate of change of temperature.
In an embodiment, the processor makes a plurality of temperature measurements corresponding to different times and calculates at least one temperature difference between a first temperature measured at a first time and one or more second temperatures measured at one or more respective second times where each of the times is bounded by a single preselected time interval and the current flow in the electric circuit occurs when one of said temperature differences as compared to a respective trigger value indicates that fluid has been demanded from the pipe. In some embodiments, a plurality of temperature differences are measured within the preselected time interval. And in some embodiments the processor updates at least one trigger value based on a comparison of the trigger value to historical temperature differences inferred from data saved in a memory device that is in signal communication with the processor. In yet other embodiments, the preselected time interval is in the range of about 0.1 to 15 seconds and the trigger values lie in a range of about 0.001 to 100 degrees Fahrenheit. In another embodiment, the sensor is a non-contact temperature sensor such as an infrared sensor.
In some embodiments the first pipe is a hot water pipe in a hot water circuit, the hot water circuit is in fluid communication with a pump and a valve, the sensor senses temperature at a location on the outer surface of the first pipe, and the valve is operative to demand hot water from the hot water circuit and the electric power circuit is operative to actuate the pump in response to the hot water demand. In some embodiments, the sensor is an infrared temperature sensor and invention includes a means for deactivating the pump. And in some embodiments the processor saves in a memory device an indication of at least a first time on a first day when hot water is demanded from the hot water circuit and the processor actuates the pump on a second day subsequent to the first day at a second time which differs from said first time by a first predetermined time difference. And in an embodiment, on a day subsequent to the first day the processor makes the first time indication previously saved in the memory device ineffective to actuate the pump when hot water is not demanded between a fourth time and a fifth time, said fourth and fifth times differing from said first time by respective second and third predetermined time differences. In an embodiment the pump is a recirculation pump.
And in some embodiments, the first pipe supplies cold water to a water heater, a second pipe is a hot water pipe in a hot water circuit, the hot water circuit is in fluid communication with the water heater, a pump and a valve, the sensor senses the temperature at a location on the outer surface of the first pipe, said location being proximate to said hot water heater and the valve is operative to demand hot water from the hot water circuit and the electric circuit is operative to actuate the pump in response to the hot water demand. In an embodiment the sensor is an infrared temperature sensor and the invention includes a means to deactivate the pump. In some embodiments the processor saves in a memory device an indication of at least a first time on a first day when hot water is demanded from the hot water circuit and the processor actuates the pump on a second day subsequent to the first day at a second time which differs from said first time by a first predetermined time difference. And in some embodiments on a day subsequent to the first day the processor makes the first time indication previously saved in the memory device ineffective to actuate the pump when hot water is not demanded between a fourth time and a fifth time, said fourth and fifth times differing from said first time by respective second and third predetermined time differences. In an embodiment the pump is a recirculating pump.
And an embodiment includes a sensor for sensing a temperature that varies with the temperature of the fluid, a processor in signal communication with the temperature sensor and a time base, the processor for making a plurality of temperature measurements corresponding to different times and for calculating at least one temperature difference between a first temperature measured at a first time and one or more second temperatures measured at one or more respective second times subsequent to said first time where each of the times is bounded by a single preselected time interval; and, the processor causes an electrical current to flow in an electric circuit when one of said temperature differences as compared to a respective trigger value indicates that fluid has been demanded from the pipe.
In still another embodiment, the pipe is in fluid communication with a hot fluid source and the sensor is an infrared temperature sensor located adjacent to the pipe and proximate to the hot fluid source.
In yet another embodiment the present invention carries out the steps of transporting hot water in a first pipe in fluid communication with a potable hot water source and a hot water valve, measuring a plurality of temperatures corresponding to different times with an infrared temperature sensor in signal communication with a processor said temperatures being measured at a location on an outer surface of a second pipe transporting cold water to the hot water source, varying the temperature of the location on the outer surface of the second pipe by opening and closing the valve, calculating a time rate of temperature change and signaling a recirculating pump to transport water from the first pipe to the hot water source when the time rate of temperature change exceeds a preselected trigger value.
The accompanying description provides in combination with the specification and the claims a description of the invention:
FIG 6 is a state transition diagram of an embodiment of a control strategy.
While specific embodiments are discussed below, it should be understood that this is done for illustration purposes only and that other components and configurations can be used in accordance with the systems and methods described herein without departing from the spirit of the invention.
In another embodiment, temperature sensing is accomplished using a non-contact sensor. A non-contact sensor measures the temperature of a surface without physical contact with the surface. Such a sensor can operate by measuring radiant energy or infrared emissions of a surface. An example of such a sensor is an infrared thermopile detector manufactured by Melexis of Belgium, type MLX90247. An advantage of a non-contact sensor is that it has very low thermal mass and can therefore respond quickly to changes in sensed temperature.
In one embodiment, the rate of change of temperature at the outside surface of a location in a piping system is used to detect flow of fluid through the inside of the pipe. In one embodiment, this flow indicates demand for the fluid at a remote location.
Connection 102 provides data from the sensors to the processor 105. Connection 102 can be of suitable length to allow the sensors to be located as needed within the plumbing system while remaining at a proximate location. For example, in one embodiment a temperature/flow sensor is located to sense the surface of a hot water delivery pipe near the outlet of the hot water heater and a pair of wires connects the sensor to the controller. In another embodiment a temperature/flow sensor is located at the return of a recirculation system into a hot water heater. In one embodiment a temperature/flow sensor is located to sense the surface of a cold water pipe providing water to the hot water heater. In one embodiment, connection 102 can be implemented as a wireless connection.
Display 103 is used to indicate information to the user. Information can include for example, status, faults, and system modes. In one embodiment display 103 is a multi-line character display, such as a liquid crystal display (LCD). In another embodiment, the display 103 is an array of light emitting diode (LED) devices. These may be any combination of single color or multi-color LEDs. Multi-color LEDs can be made to change color under processor command, thus using color to indicate information to the user. LEDs can also be made to glow steady, blink, or flash in various patterns to communicate to an observer, all under command of the controller 105. In one embodiment display 103 is a single monochromatic LED that uses various modes of steady-on, steady-off, or patterns of on and off to indicate information. Connection 104 provides signals to the display 103 from the controller 105.
Processor 105 controls the various outputs of the system in response to predetermined algorithms and in response to data that can include input from sensing system 101 as well as time rate of change and histories of sensed parameters. The outputs of the processor 105 can include setting the power switch 114 to an off or on state, driving the display 103, and setting the state of the remote pump connection 117.
The processor 105 can be implemented in many ways, all in accordance with the descriptions herein. The processor can also be described by terms such as controller, microcomputer, digital computer, analog computer, or threshold detector. In one embodiment processor 105 is a collection of analog electronics. Control algorithms are implemented by selection of components, circuit topology and operational amplifiers and comparators.
In another embodiment, processor 105 includes a digital microcontroller or processor executing a set of instructions stored in memory. The set of instructions are sometimes referred to as software, firmware, or a program. The processor executes software that implements predetermined sensor data gathering, decision, and control algorithms. In one embodiment the processorer function is provided by a PIC16F676 microcontroller combined with support circuitry. The PIC16F1676 is manufactured by the Microchip corporation of Santa Clara, Calif.
In one embodiment a time base is included in processorer 105. A time base can provide measurements of intervals and is useful in determining rate of change of a value over a time interval. A time base can be implemented using digital components such as counters or timers. A time base can also be implemented in non-digital or analog circuit, for example by observing the time varying voltage of a charging capacitor.
In one embodiment processor 105 can perform functions requiring storage of parameters or events. A memory 107 and data storage and retrieval means 106 is provided to accomplish these functions. In one embodiment the memory 107 and controller 105 are contained in a single integrated circuit along with interconnection 106. In another embodiment the memory 107 is in a separate package from processor 105. Several types of memory 107 may be provided, all in accordance with the present invention, including random-access memory (RAM), electrically erasable programmable memory (EEPROM), FLASH memory, disk storage, or any other means providing for storage and retrieval of data by the controller 105. In one embodiment the memory contains software for the controller that can be changed without removal or replacement of the memory. Thus the controller program and associated algorithms can be easily changed, for example to fix problems, add features, improve software, or modify algorithms or constants.
The system 100 is connected to a source of electrical power by input power connector 112. The power is made available within the system by power wiring 113. Power wiring 113 brings the input power to power supply 109, phase detector 111, and the input of power switch 114. Power supply 109 provides power to the components of the system. Power connections from power supply 109 to individual components are not shown in
In one embodiment, the power input 112 is connected to a source of 120 volt, 60 Hz. alternating current (AC) commonly available in the United States and other countries. The power supply converts one hundred twenty volts AC to five volts direct current (DC) usable by controller 105, sensors 101, display 103, memory 107 and phase detector 111.
Control of an external pump is provided by controllable power switch 114. Power switch 114 can be turned on or off by processor 105 using connection 110. When power switch 114 is set to the on state, the output power wiring 115 is energized and power is available at output power connector 116. In one embodiment current flows through circuit 114 in response to demand detected using time rate of temperature change. In one embodiment the connector is a receptacle into which a power cord for an external device can be connected. For example, a recirculation pump power cord can be connected. In another embodiment, the pump controller 100 is integrated into the pump mechanically and electrically so that pump power output 116 is wired directly to the pump. In one embodiment, power switch 114 is a solid state relay, model number PR21HD2NSI, manufactured by the Sharp Corporation.
In some situations it is desirable to provide a signal 117 to external systems that is activated simultaneously when the power switch 114 is commanded to the on state. A remote pump activation signal 117 is provided for this purpose. Thus signal 117 is an electric circuit responsive to time rate of temperature change. Signal 117 may be a voltage-level signal, switch closure, pulse, relay output, open collector transistor, or any control signal appropriate for activating the desired remote device. In one embodiment, current flow in circuit 117 signals hot water demand.
Phase detector 111 is provided in certain embodiments, where the input power supply 12 is a source of alternating voltage. The phase detector 111 can provide several features to the system. In one embodiment, the phase detector 111 derives a periodic clock signal from the repetitive alternating cycle of the input power source by detecting certain repetitive phase characteristics of the input power at connector 112 and wiring 113. An example of such a characteristic is a zero crossing, in which case the phase detector may also be called a zero crossing detector.
In one embodiment the phase detector 111 detects zero crossings of a 60 Hz. sinusoidal voltage to produce a 120 Hz clock signal. A clock signal is produced each time the input crosses zero voltage. A 60 Hz sinusoidal voltage crosses zero 120 times each second. The power input frequency is often very accurate and stable, and a clock derived from the power frequency can be very accurate. The controller 105 can use an accurate clock for many functions.
Another feature that can be provided by phase detector 111 and controller 105 is activation or deactivation of the pump via control switch 114 at certain phase angles of the AC power supply. It can be desirable to activate the pump at zero voltage, peak voltage, zero current, or some other selected phase angle of a sinusoidal AC voltage or current input. Activation of the pump at selected phase angles can reduce interference, extend pump life and provide other benefits.
In one embodiment, pump switching at a desired phase angle of the AC input waveform is provided by a zero crossing detector combined with an interval timer. The phase detector 111 detects zero crossings of the input power and then waits a predetermined period of time to switch the pump. For example, if it is desired to switch at the peak of a 60 Hz waveform, it can be calculated that the peak voltage magnitude occurs approximately 4.17 milliseconds after each zero crossing.
With reference to
A temperature sensor 204 is placed on the hot water piping 203 at a location where it is desired to detect flow of hot water according to the present invention. This sensor measures the outside surface temperature of the pipe and can be mounted without cutting or modifying hot water piping 203 in any way.
When a user desires hot water, he or she opens the valve (e.g. 205, 207, 209) corresponding to the location where water is desired and hot water flows from the heater 202, through piping 203, to the outlet (206, 208, 210) corresponding to the opened valve.
When hot water is not being demanded, i.e. none of the valves 205, 207 or 209 are opened, water in hot water piping 203 cools because after the hot water and pipe are typically hotter than the surrounding ambient temperature and heat is radiated or conducted away. Thus the temperature measured by sensor 204 decreases over time when there is no demand for hot water.
When hot water demand is subsequently indicated by a user opening one or more of valves 205, 207 or 209, hot water will flow from heater 202 into piping 203 and past sensor 204. This water will typically be at a higher temperature than the water in the pipe when no demand is present. Thus the hot water flow caused by demand will cause the pipe 203 temperature to rise along the path of water flow. This will cause a rise in temperature at sensor 204 over time. In this way time rate of change of temperature at sensor 204 can be used to detect demand for hot water.
A key aspect of this scheme is that only the rate of change of the measured temperature is needed. The temperature value itself is not important. In one embodiment, the temperature sensor is not calibrated and no temperature value is calculated in conventional units such as Fahrenheit or Celsius. The sensor is used only to note rate of change over time.
In one embodiment, the temperature sensor is a thermistor. Thermistors change resistance with temperature. The resistance as a function of temperature for a thermistor is typically monotonic but non-linear, requiring conversion to a linear scale when a temperature value is needed in conventional units. But according to the present embodiment, absolute temperature is not needed, thus the non-linearity of the sensor is not significant. This allows use of less expensive sensors and requires less signal processing of the sensed value when it is desired to detect demand for input to a controller.
In another embodiment, the temperature sensor is a non-contact sensor such as a device sensitive to infrared radiation on a surface not physically touching the sensor.
The scheme just described can also be used as a simple but effective communication mechanism. This communication system uses the flow of hot water as the signaling medium. The valve is the sending device and the temperature sensor the receiving device. For example, again with reference to
In one embodiment, this communication mechanism is used to signal a demand for hot water. According to this embodiment, a user who desires hot water opens a valve at the location where hot water is desired, allows a small amount of water to run, then closes the valve. This sends a message to the temperature sensor 204 that is in turn used to activate a hot water delivery system. The user, after opening and closing the valve to send the hot water request, waits for a short period of time for the hot water recirculation system to supply hot water. The user than opens the valve and uses hot water normally.
In this manner, any valve, faucet, or tap outlet of a hot water system can be used both to obtain hot water and also to signal a hot water delivery system indicating that hot water use is desired.
This scheme has several advantages. No special installation is required on conventional systems. The signaling device, i.e. the faucet, is a component of conventional plumbing systems and requires no additional components, power source, or redesign. The receiving device is easily installed on existing piping by attaching to the pipe exterior surface and requires no plumbing or modification. No wiring is required to connect the receiver to the transmitter.
In addition, the system is easy to learn to use as the actions required are part of the familiar process of using hot water at a conventional outlet. Another advantage is that the system can be used in a conventional manner or by a person untrained in using the faucet as a signaling device. In this way an untrained person or unfamiliar guest can open a faucet and let it run and the receiver will detect demand and receive hot water promptly.
It can be appreciated that there are many ways to detect demand for a fluid in a fluid supply system because demand causes flow of fluid past many locations in the system.
With reference to
Not shown in system 320 are a number of check valves sometimes installed to prevent water flow in inappropriate directions in the system. Those familiar with the art will readily identify locations and functions for these valves.
With reference to
In another prior art approach, still with reference to
It can be appreciated that there are many sensor configurations and locations that can be used to detect flow in a plumbing system, and that not all possible sensors will be present in every embodiment. Referring to
Sensor 381 can be located on a pipe in the hot water system proximate to the outlet of the hot water heater HW. A location is proximate if it allows the sensor to detect flow promptly and reliably. For a typical structure there are many proximate locations on the contiguous plumbing network.
In one embodiment sensor 382 detects flow of hot water in the return piping segment of the recirculation system. Sensor 382 can be a temperature sensor used in conjunction with processor 384 to open switch 385 and stop pump P when hot water has filled the system. Sensor 382 is shown close to pump P, but may be located at any point in the hot water system needed. Generally the location of sensor 382 is chosen to include all outlets between the sensor and hot water heater. In many systems ease of installation makes it desirable to install sensor 382 proximate to the pump or to the hot water heater.
In one embodiment, sensor 382 is used in conjunction with controller 383 to detect that the pump should be shutoff by noting a positive temperature rate at sensor 382, followed by a near-zero temperature rate at sensor 382.
In another embodiment, sensor 383 detects hot water demand. Sensor 383 is mounted proximate to the cold water inlet to hot water heater HW. Such a sensor can be used to detect hot water demand since the exit of hot water from the hot water heater is replaced by an inflow of cold water flowing by sensor 383. The cold water flow can be detected by the negative rate of temperature change at sensor 383.
In one embodiment, sensors producing data for plots 401 and 402 can be temperature sensing devices. However it is a significant feature that the methods described rely on changes in temperature, and this can be executed without regard for actual temperature values in conventional units, such as Fahrenheit or Kelvin. It is also a feature that the controller does not rely on set points expressed in conventional units.
With regard to plot 400, three instants of times are called out: tX 403, tY 404 and tZ 405. Plot 401 shows the temperature of a location near the outlet of a hot water heater, as sensor 381 in
In
At time tY 404 a positive rate of change is seen at the return path of the recirculation line, as can be seen in plot 402. This indicates some hot water is being returned to the hot water heater and that the hot water circuit is nearly filled with hot water due to the preceding activation of the recirculation pump.
At time tZ 405 the hot water return line plot 402 has reached a steady temperature after a rising temperature starting at time tY 404, indicating the system has reached a steady-state maximum temperature. At this point in time the hot water supply line and recirculation line are filled with hot water.
In one embodiment, the control strategy described above is implemented by use of two temperature sensors, one placed to sense the data corresponding to plot 401, and the other corresponding to plot 402. Thus the control strategy can be executed as described.
In another embodiment, the control strategy described above is implemented using a single sensor, at a location corresponding to plot 401. This embodiment uses the data from sensor location corresponding to plot 401 to start the pump in response to demand, and uses an estimate of the time required to fill the system with hot water, shown as tPUMP 406 in plot 400 to determine when to turn off the pump. In one embodiment, the estimate of tPUMP is predetermined.
In another embodiment the system is initially installed connected with two sensors, allowing measurement and storage of system parameters such as tPUMP 406. If a sensor at location corresponding to plot 402 subsequently fails, the system can continue to operate using sensor at location corresponding to location 401 and previously measured tPUMP 406.
A problem can arise when using analog-to-digital converters for measuring rates of change over time. Analog-to-digital converters only provide a limited number of discrete spaced input voltage detection levels, each corresponding to a numerical output value. For a slowly changing signal, i.e. a low rate signal, the signal may not change enough between samples to cause the numerical output value to change. The samples can be taken further apart in time, but this slows down the detection for rapidly changing signals.
The present invention can overcome the problems with conventional analog-to-digital conversions calculating rates described above. In one embodiment the processor makes temperature measurements continuously and stores a number of the most recent samples. Then several differences are calculated. In one embodiment the change over the last sample period, the last two sample periods, and the last four sample periods are all calculated. The difference between a more recent sample and the latest sample provides fast detection of rapidly changing signals. Differences between the latest sample and data samples further in the past detects slowly changing signals that may take several sample periods to change enough to cause the digital output of the analog-to-digital converter to change significantly.
In another embodiment, the sensor data 402 shown in
As described herein, both a temperature-regulated and a demand regulated control mode can be implemented to control a recirculation pump. Each mode can be desirable in certain situations. Temperature regulated mode provides ready hot water, but wastes energy in periods of no demand. Demand regulated mode saves energy but requires slightly longer for delivery of hot water, as compared to temperature regulated mode.
A solution is to provide a controller able to execute the algorithms of both modes, with additional functionality provided to select between the modes and transition between the modes, a multi-mode controller. One embodiment of this multi-mode control scheme is illustrated in
Economy, or demand-controlled mode state 601 executes when the pump is off and the system is awaiting a detected flow of hot water to activate the pump. This is an economical mode suited for most times. When demand is sensed, the controller traverses transition 607 and pump-on state 606 is executed, activating the recirculation pump.
Transition 604 is traversed when the hot water system is filled, or in one embodiment when a time limit has been exceeded. Transition 604 causes the controller to execute in temperature controlled-mode state 603. In temperature-controlled mode, the system can be activated by demand for hot water, or by falling temperature in the system, both conditions cause the controller to traverse transition 605. Thus in temperature controlled-mode hot water is readily available at all times.
After a predetermined period with no demand while in temperature-controlled mode state 603, the controller traverses transition 602 and executes demand-controlled mode state 601.
In one embodiments the predetermined time periods used as transition criteria for transitions 602 and 604 are determined as constants in the controller software program. In another embodiment, the time periods for transitions 602 and 604 can be adjusted during system operation in response to sensed conditions. Thus the time periods are adaptive over time.
In one embodiment, temperature controlled mode is selected for a period of time after pump activation and demand mode is selected after a period of time has elapsed with no demand. This is based on the principle that hot water is often used several times in near succession. Thus energy is saved in periods of no demand while hot water is readily available in periods of frequent demand.
The pump runs until a rise in temperature is seen at the recirculation return, in decision 503. Following a rise, a steady-state value, or leveling-off, is waited for in decision 504. When temperature has reached a steady state value, it is recorded in operation 505, the pump is stopped in operation 506, and the controller returns to decision 501 awaiting demand once again.
The system then waits for either a rising temperature in decision step 523 or the timer to reach a predetermined maximum value in decision 524. When either of the criteria in decisions 523 or 524 are satisfied, the algorithm proceeds accordingly.
If the maximum pump time is reached then decision 524 is true and operation proceeds to step 529, stopping the pump. The system then returns to step 520 to await demand.
Alternatively, if decision 523 is true because temperature is rising at the recirculation return, the controller then waits for either the rising temperature value to reach a steady-state value, satisfying the criteria in decision 526, or the maximum pump time to be reached in decision 528. If the maximum pump operation time is reached, satisfying decision 528, the pump is stopped in operation 529 and the controller returns to step 520.
Alternatively, if the temperature has reached a steady-state value, satisfying the decision criteria in decision 526, the controller then executes decision 527, determining if the pump has operated for a predetermined minimum time period. If the pump has not operated for the minimum time, the algorithm remains in decision 527 until the time period is complete. Eventually the time period will reach the predetermined value and the decision criteria 527 will be satisfied. The algorithm then proceeds to turn off the pump in operation 529 and return to decision 520 awaiting the next demand. In another embodiment, a delay is inserted between operation 529 and decision 520 to ensure a minimum time elapses between subsequent pump activations.
Another embodiment is illustrated in
With reference to
When the timer has completed the pump is deactivated in step 534. In step 535 a timer is set and started. This timer serves to prevent the pump from restarting too soon after operating. In one embodiment this timer value can be zero so decision step 536 is essentially skipped. In other embodiments the timer value can be non-zero and decision block 536 is executed until the timer finishes.
After exiting decision block 536, the system returns to block 530 to await demand. In one embodiment an adaptive control scheme observes demand patterns and anticipates future demand based on past demand. It can be appreciated that this scheme can detect demand in many ways in accordance with the features and descriptions herein. For example, demand can be sensed by the flow sensors and algorithms described herein. Demand may also be detected by a motion detector, push button or other demand indication device.
In one embodiment, the system can include a timekeeping system. The timekeeping system generates a time-tag value that varies from 0-23 hours and recycles every 24 hours. The system can also generate a day-tag value that varies from 0-6 days and recycles every 7 days. This system is similar to a clock and calendar, but with significant differences. One way this system differs from a conventional clock and calendar is that it is not necessarily synchronized with any external or standard clock or calendar, but instead simply counts time from the moment power is first applied to the controller. In this way, a unique day-tag and time-tag is generated that can be used to store and recall controller events relative to one another, without reference to any outside time. This scheme has an advantage in that it does not require setting or synchronization to any outside clock. It also has the advantage of not requiring any adjustment for daylight savings time or time zones. Another advantage is that the system does not require any external interface, switches, buttons, or input devices since no external input is required for operation.
In one embodiment, the time-tag has a resolution of one minute, and the corresponding counter continuously counts from zero to 1439 and recycles, resuming the count from zero. There are 1440 minutes in a 24 hour period, thus a unique counter value is generated for each minute of a day. If the counter is observed at the same time of day on different days, it will have the same value. For example, if the time-tag counter value is 225 at 6 a.m. on Tuesday, it will have the value 225 at 6 a.m. on Wednesday and all days of the week until the controller loses power, within the accuracy of the counting system. Similarly, a day-tag counter will have a resolution of one day, so will count from zero to six and then recycle. For example, if the day-tag counter has a value of 3 on a certain Saturday, it will always have the value 3 on any Saturday.
The generation of time-tag and day-tag can be used to provide a capability for adaptive control. It is generally the case that hot water systems are used according to certain pattern of human behavior. It is an advantage that the system described herein can observe those patterns and control the recirculation system in accordance with the observed patterns.
For example, suppose the members of a family awaken and shower every weekday morning starting at times between 6 a.m. and 6:30 a.m. This can be determined by observing the pattern of demand for hot water during several days, correlated against time-tag and day-tag values. Thus the controller can activate the recirculation system so hot water is available each weekday at 6 a.m. Although the controller will not be aware that the time of activation is called 6 a.m. by those observing external clocks, it will be able to provide hot water at a consistent time each day. Similarly, the controller can be programmed to be aware that five of the seven days are weekend days, and to recognize and predict usage patterns accordingly.
Similarly it is a feature that the controller adaptive capability includes observation of variation from a pattern. In the above example, the members of a family begin to use hot water at times that vary between 6 a.m. and 6:30 a.m. on different weekdays. In one embodiment the controller is programmed to understand that these usage events on different days are related as variations on a morning usage pattern, and that the earliest event should govern the activation of the pump.
This application claims the benefit of U.S. Provisional Patent Application 60/672,159 filed Apr. 15, 2005 and entitled “SYSTEM AND METHOD FOR EFFICIENT AND EXPEDIENT DELIVERY OF HOT WATER.”
Number | Date | Country | |
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60672159 | Apr 2005 | US |