MXPA98006695A - Water heater with proportional band temperature control for better thermal performance - Google Patents

Abstract

The present invention relates to a water heater having a water tank and an electrical resistance heating element that extends inside the water tank to heat the water in the tank, the water heater includes a band temperature controller proportional to conduct electrical energy to the electrical resistance heating element in discharges, each discharge of electrical energy is followed by a period during which the temperature controller does not conduct energy to the electric resistance heating element, in one embodiment, each discharge of electrical energy lasts approximately 95% or less of a cycle consisting of a discharge of electrical energy followed by a period during which the temperature controller does not conduct electrical energy

Description

WATER HEATER WITH PROPORTIONAL BAND TEMPERATURE CONTROL FOR IMPROVED THERMAL PERFORMANCE FIELD OF THE INVENTION The present invention relates generally to electrically heated water heaters. Particularly, the invention relates to improved methods and apparatus for heating water in such water heaters. More particularly, the invention relates to methods and apparatuses for pulsing electrical energy to a heating element of electric resistance in order to improve the performance of the heating element in a water heater. The description herein refers to domestic water heaters where the water is heated with electrical resistance heating elements. The description, as well as the improvements of the present invention, are generally applied to water heaters employing electrical resistance heating elements.

BACKGROUND OF THE INVENTION A hot water heater »as contemplated herein, typically comprises a vertically mounted» cylindrical water tank permanently covered, a cylindrical shell coaxial with and radially spaced from the water tank to form an annular space between the outer wall of the water tank. water tank and the inner wall of the frame, and insulating material in at least a portion of the annular space to provide insulation; thermal ation to the water tank. Polymer foam extended directly into the annular space is an effective insulating material. Particularly, the polyol and isocyanate reagents with foam agents are commonly reacted within the annular space to form polyurethane foam which expands easily to fill the available space and cures quickly in a hard closed cellular foam insulation material. Means are provided such as foam dams, to contain the foam that expands within the annular space. The water tank has various accessories such as an inlet, an outlet and drain accessories. Especially, the water tank is provided with water heating means and temperature control. Typically for electrically heated water heaters, the water heating means comprises a heating element of electrical resistance. The heating element extends through an accessory in the wall of the water tank such that the resistance heating element is inside the tank and the means for connecting the resistance heating element to a source of electric power are outside the tank of water. The temperature control means for an electrically heated water heater commonly comprise a mechanical thermostat that operates a switch to allow the passage of electrical energy through the electrical resistance heating element when it is detected that the water in the tank is below of a prescribed selected temperature "and operates the switch so that the electrical energy does not pass through the heating element of electrical resistance when the water in the tank is above the prescribed temperature. With such means of temperature control, the electrical energy through the electrical resistance heating element is either completely switched on by "passing full electric current" or completely disconnected. The mechanical thermostats commonly used for water heaters include a bimetallic metal disk that is mounted in contact with the external wall of the water tank to detect the temperature of the water in the water tank. The bimetallic disk »when it is colder than the prescribed temperature» is in a flat position. However, at the prescribed temperature the bimetallic disk is placed abruptly in a convex dome shape which is maintained until it is cooled to a temperature below the temperature prescribed At a temperature below the prescribed »the bimetallic disk is again placed in a flat position. The mechanical hysteresis in the bimetallic disk causes the temperature at which the disk is placed flat again to be substantially lower "(5 to 10 ° W) than the prescribed temperature at which the bimetallic disk is abruptly placed in the form of convex dome The bimetallic disk is connected to an electrical switch in a phenolic resin frame attached to the external wall of the water tank by means of an electrically isolated drive rod. electrical line that connects the electric resistance heating element to a source of electrical power A threaded contact pin is mounted on the frame in contact with the bimetallic disc for manual regulation of the tension on the bimetallic disc such that the bimetallic disc it can be adjusted to abruptly stand from a flat position to a convex dome position to the Desired prescribed temperature When the bimetallic disc detects a cold water temperature, and the disk is in a flat position »the drive rod closes the electric switch, allowing electrical energy to flow through the electric resistance heating element» thus heating the water in the water tank. As the water warms up »the bimetallic disk is abruptly placed in a convex dome at the prescribed temperature and the drive rod opens the electrical switch» disconnecting power to the electrical resistance element. The electrical switch remains open and the power disconnected until the water in the tank is cooled sufficiently for the bimetallic disk to be placed in a flat position, thus closing the electrical switch and allowing electrical energy to flow into the heater. of electrical resistance. Electric power is either completely connected or completely disconnected. Due to variations in the fabrication and hysteresis of the bimetallic disk, the temperature at which the disk will abruptly be placed from a flat position to a convex dome-shaped position can vary as much as 25 ° F (14 ° C). Tension can be applied to the bimetallic disc through the threaded contact pin to regulate the prescribed temperature at which the bimetallic disc will abruptly be placed from a flat position to a convex dome-shaped position. The threaded contact pin is not calibrated »and the voltage adjustments to achieve the bimetallic disc drive at a selected prescribed temperature are carried out by trial and error. Frequently a mechanical temperature control using a bimetallic disk ter, "exceeds" the desired prescribed temperature "allowing the electrical resistance heating element to continue heating the water in the water tank above the prescribed prescribed temperature. The mechanical temperature control means "described above" and the electrical resistance heating element are in contact with the outer wall of the water tank and extend into the annular space between the external wall of the water tank and the frame. These items must be accessible for maintenance. One or more openings in the frame wall provide access to the temperature control means and the electric resistance heating element. A dam structure is provided around each opening to protect the temperature control means and electric resistance heating element from contact with the insulating foam and prevent the foam from escaping from the annular space through the openings in the frame wall . Electrically heated water heaters are provided with safety devices. A high temperature safety shut-off switch is installed in the power supply line that cuts power to the electrical resistance heating element when the temperature in the water tank rises above a permissible level. In addition the water tank is provided with a high temperature safety valve that is set to open at approximately the boiling point of the water »(100 ° C)» to prevent an increase in pressure in the water tank of the water in ebul 1 ición.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention. The electrical energy to a heating element of electrical resistance of a water heater is modulated by providing electric power in short pulses or discharges over a substantial portion of the water heating cycle. Modulating the electric power improves the heating efficiency of the water in the water heater. Providing electric power to the resistance heating element of an equal water heater up to a prescribed temperature to substantially the same velocity as with a mechanical temperature controller of the prior art, however, it uses substantially less electric power to heat the water. The electric hot water heater used to heat and store water in a typical residential installation is often the largest single electrical appliance for energy consumption. In this way, using substantially less electrical energy to heat the water provides significant energy and cost savings. A preferred way to modulate electric power in short discharges to the resistance heating element is through the use of a proportional band temperature controller. A proportional band temperature controller is an electronic device that detects the temperature of the water in the tank of a B water heater and controls the electrical energy to the resistance heating element at a speed that depends on the differential separation of the water temperature from a prescribed prescribed temperature. The proportional band temperature controller modulates the electrical energy to the electric resistance heater element by providing electric power in cycles. Each cycle comprises conductive electric power in a short discharge followed by a short period without electric power conduction. When the differential separation between the temperature of the water in the water tank and the prescribed temperature is large, the period during which the electric power is conducted in each cycle is long compared to the period during which the electric power is not driven. As the temperature of the water approaches the selected prescribed temperature, the period during which the electrical energy is conducted to the heating element of resistance in each cycle becomes shorter. The period for each cycle can be regulated and typically is less than one second. In addition »typically» the period of each electric discharge during a cycle is reduced from about 95% to about 50% of the cycle period as the temperature of the water approaches the prescribed temperature. When the water temperature reaches the prescribed temperature »the proportional band temperature controller completely stops conducting electrical energy to the resistance heating element. Then »when the water temperature drops below the prescribed temperature» the proportional band temperature controller again conducts electrical energy to the resistance heating element in short discharge cycles. Proportional band temperature controllers are efficient with very small electrical energy losses "and stop conducting electrical power accurately when the water temperature reaches the prescribed temperature. In addition, proportional band temperature controllers are less expensive to manufacture and install compared to the mechanical temperature controllers of the prior art. In addition »aggregates such as indicator lamps» audible alarms »and temperature indicators» can be easily connected to the proportional band temperature controllers to improve the operation and ease of use of the water heaters to which they are connected. Other aspects and advantages of the invention will be apparent to those skilled in the art upon review of the following detailed description, claims and claims.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a sectional view of a water heater »showing the arrangement of the temperature control of the present invention with respect to other component elements of the water heater; Figure 2 is a schematic of the preferred temperature controller of the present invention; Figure 3 is a graph of energy consumption data of a mechanical temperature controller of the art and a proportional band temperature controller of the present invention; and Figure 4 is a graph of data of the power consumption ratio of the mechanical temperature controller of the prior art and the proportional band temperature controller of the present invention. Before explaining an embodiment of the invention in detail, it should be understood that the invention is not limited in its application to the details of construction and the arrangement of component elements or steps that are set forth in the following description or illustrated in the following. drawings. The invention is capable of other embodiments and of being practiced or carried out in various other ways. In addition, it should be understood that the phraseology and terminology used herein have the purpose or purpose of the description and should not be viewed as lim tat as.

DESCRIPTION OF THE PREFERRED MODALITY As described above, the use of a proportional band temperature controller in a water heater having an electric resistance heater element has the unexpected advantage of heating water in the water heater to a preset preset temperature while consuming at the same time less electrical energy consumed by heating the same weight of water to the same temperature prescribed in the same water heater using a mechanical temperature controller of the prior art. A proportional band temperature controller is an electronic device comprising a water temperature sensing device (thermistor). a prescribed temperature device (variable rheostat), a thyristor commanded to transfer electrical energy to the resistance heating element, and a logic circuit for controlling the thyristor in response to signals from the water temperature sensing device and the prescribed temperature device. The logic circuit receives a voltage input signal from the water temperature sensing device and the prescribed temperature device which indicates the differential of the water temperature of the prescribed temperature. The logic circuit, in response to the voltage input signals of the water temperature sensing device and the prescribed temperature device »sends signals to the controlled thyristor. At large temperature differentials between the water temperature sensing device and the prescribed temperature device, the logic circuit sends signals to the controlled thyristor to conduct electricity during a main portion of approximately 94%. of each cycle of alternating current »and sends signals to the ordered thermistor that stops conducting electricity for approximately 6% of each cycle of alternating current. As the temperature differential between the water and the prescribed value becomes smaller, the temperature of the water enters a temperature control band where the logic circuit begins to exert more control over the thyristor commanded to limit electrical energy to the heating element. resistance. When the water temperature enters the proportional control band, the logic circuit establishes a new control cycle period and sends signals to the thyristor to conduct electrical energy for a B5% of each cycle and stop driving for 15% of the cycle. each cycle. As the water temperature approaches the prescribed temperature the logic circuit sends signals to the thyristor to drive less than each cycle period. When the temperature of the water reaches the prescribed temperature »the logic circuit closes the thyristor and no electrical power is supplied to the resistance heating element until the water temperature falls again below the prescribed temperature. To avoid excessive cyclic variations over the prescribed temperature, the logic circuit is set to require the water temperature to fall from 5 ° C to 10 ° C below the prescribed temperature before the thyristor receives the driving signal again electrical energy and heat the water back to the prescribed temperature. This improvement in water heating efficiency in the water heater using a proportional band temperature controller is not fully understood. In theory, the entire electrical energy supplied to a resistance heating element will become heat, and that heat must be transferred to the water surrounding the resistance heating element. The same amount of electrical energy must heat the same weight of water the same amount of temperature degrees. As shown in the following example, a water heater that features a proportional band temperature controller requires approximately 10% less electrical energy to heat a water tank to a selected prescribed temperature than the same water heater that presents a mechanical temperature controller of the prior art. The improved accuracy of a proportional band temperature controller to bring the water to a prescribed temperature with little excess response partly explains the improved efficiency over a mechanical temperature controller "but does not seem to explain everything. While I do not wish to be limited, I suggest that the improvement in heating efficiency by using a proportional band temperature controller arises from physical conditions within the water tank affecting the heat transfer of the water resistance heating element. A proportional band temperature controller conducts electrical energy to the resistance heating element in short discharges followed by short periods during which electrical power is not conducted until the water in the water tank reaches a selected prescribed temperature. The proportional band temperature controller stops accurately driving the electrical energy to the resistance heating element when the water reaches the prescribed temperature. On the other hand, a mechanical temperature controller of the prior art conducts electrical energy to the heating element of full power resistance as the water heats up. When the water reaches the prescribed temperature the mechanical characteristics of the bimetallic thermocouple can cause the mechanical temperature controller to overflow and heat the water to a temperature above the prescribed temperature before it stops conducting electrical power to the heating element of the heating element. sten A resistance heating element, as used in domestic hot water heaters, heats up in a few seconds to a temperature in the range of B00 ° F to 900 ° F. The water, in contact with such a heating resistance heating element, is vaporized to form a vapor layer around the resistance heating element and by reducing the heat transfer of the water resistance heating element. With a mechanical temperature controller, the resistance heating element is heated in this manner and remains at an elevated temperature until the bimetallic thermocouple disconnects the electrical energy. The excess heat of a resistance heating element controlled by a mechanical temperature controller can be radiated to the wall of the water tank »or it can be transported by steam to the top of the water tank where excess heat is absorbed in the water tank. the highest layer of water that is located away from the thermocouple bimetallic temperature detector. With a proportional band temperature controller »the resistance heating element is heated during each discharge of electrical energy and cooled by contact with water during periods between discharges. This cooling of the resistance heating element between each discharge of electrical energy reduces the temperature at which the resistance heating element rises and reduces the accumulation of vapor around the heating element of hot resistance. Accordingly, the heat transfer from the heating element of water resistance increases. The supply of electric power to a resistance heating element in a water heater in discrete short discharges »each discharge followed by a period with the IS disconnected electrical power »improves the efficiency of heat transfer from the water resistance heating element in the water heater. Proportional band temperature controllers are well known and widely used in many commercial applications, including controlling water temperature in appliances such as coffee makers. In my opinion, proportional band temperature controllers have not been used to control the temperature of a large volume of water in a water heater. Figure 1 of the drawing shows a sectional view of a water heater 10 comprising a permanently closed water tank 11 »a frame 12 surrounding the water tank 11» and foam insulation 13 filling the annular space between the tank of water 11 and the frame 12. A water inlet duct or inlet tube 14 enters into the upper part of the water tank 11 to add cold water near the bottom of the water tank 11. An outlet duct of water 15 leaves the water tank 11 to remove hot water near the top of the water tank 11. The resistance heating element 16 extends through the wall of the water tank 11. The proportional band control circuits in the control unit 17 are connected to the resistance heating element ÍS. The thermistor l? »In contact with the external wall of the water tank 11 for detecting the water temperature in the water tank 11» is connected to the logic circuit by electric cables 19. Electrical AC is supplied to the thyristor sent through of the transmission line 20. A custom-made operator interface 30 mounted on the outside of the water heater communicates with the control unit 17 and provides safety protection access for control of the heating element. The operator interface is operable to provide direct or remote control of the heating element. Figure 2 of the drawings is a schematic drawing of a preferred proportional band temperature control circuit 100 for heating water in a water heater according to the method of the present invention. In FIG. 2, the resistance heating element 125 is a heating element of 4,500 watts to heat water in a water heater. The prescribed temperature device is a variable resistor to set the prescribed value of the temperature in the range of approximately 90 ° to 1B0 ° F. The thermistor 102 detects the water temperature in the water heater. In an alternative embodiment "a plurality of thermistors could be placed across the tank to measure the water temperature in a plurality of locations. The output of the thermistors could be averaged. The controlled thyristor 103 is a TRIAC »manufactured by Motorola, Inc.» to control electrical power to the resistance heating element 125. The logic chip 104 is an IB UAA1016A proportional band temperature controller manufactured by Motorola, Inc. Two hundred forty volts of electrical power is supplied to the proportional band temperature control circuit 100 through transmission lines 105 and 106. The IOS optocoupler, as described next, it controls how much the water temperature should decrease with respect to the prescribed temperature before the proportional band temperature control circuit is reactivated. A stabilized supply voltage of approximately -S volts is supplied to the proportional band temperature control circuit from the transmission line 106 through the Zener diode 107 and the resistor 109 to the transmission line 110. The voltage drops through of the prescribed temperature device 101 and the temperature sensor 102 produce a signal voltage at point 111. The signal voltage is proportional to the temperature difference between the prescribed temperature and the detected water temperature. The detected voltage is transmitted through the transmission line 112 to a circuit of a voltage comparator 113 within the logic chip 104. A reference voltagewhose magnitude is determined by voltage drops through resistors 114 and 115, is generated at point 116. A sawtooth voltage, which is generated in the sawtooth generator 11B on logic chip 104, is imposed on the reference voltage at point 119. The reference voltage, modified by the sawtooth voltage passes through the transmission line 117 to the second circuit of the voltage comparator 113. The sawtooth voltage imposed on the The reference voltage causes the voltage in the second circuit of the voltage comparator 113 to vary »in a sawtooth design» over a cycle of approximately 0.85 seconds from a minimum to a maximum voltage. In the voltage comparator 113 »the signal voltage in the first circuit is compared with the modified reference voltage in the second circuit. The comparison result is transmitted through the transmission line 120 to the logic circuit 121. In the logic circuit 121, a signal is generated to pass through the transmission line 122 »amplifier 123 and transmission line 124 to control the thyristor 103. When the signal voltage in the first comparator circuit 113 is greater than the maximum value of the reference voltage in the second circuit of the comparator 113 »the signal to the thyristor 103 is to conduct and allow the electrical energy to flow through of the resistance heating element 125 to heat the water in the water tank. The logic chip 104 is arranged in such a way that the signal on the transmission line is arranged in such a way that the signal on the transmission line 124 causes the thyristor 103 to conduct electricity for 96% of each current cycle alternate and stop driving for 4% of each current cycle.

The signal voltage in the first circuit of the voltage comparator 113 will fall to a value less than the maximum value of the reference voltage in the second circuit of the voltage comparator 113 as the temperature of the water detected by the temperature detector 102 the prescribed temperature selected in the prescribed temperature device 101 approaches. When the signal voltage lies in the range between the maximum value of the reference voltage and the average of the reference voltage value »the temperature control circuit 100 is within the range of proportional band control. Thus »when the signal voltage is greater than the value of the reference voltage in the second circuit of the voltage comparator» the logic circuit 121 sends a signal to the amplifier 123 so that it sends a signal to the thyristor 103 to conduct electrical power to the resistance heating element 125. Then »when the sawtooth voltage causes the reference voltage in the second circuit of the voltage comparator to increase to a value greater than the value of the signal voltage in the first circuit of the comparator voltage »the logic circuit 121 sends a signal to the amplifier 123 that sends a signal to the thyristor 103 that stops conducting electrical power to the resistance heating element 125. As the signal voltage in the first circuit of the voltage comparator approaches more than the average value of the reference voltage in the second circuit of the voltage comparator 113 »thyristor 103 does not conduct torque at higher percentages of each cycle of sawtooth tension generated. When the temperature of the water detected by the temperature sensor 102 is equal to the prescribed temperature of the prescribed temperature device 101 the signal voltage in the first circuit of the voltage comparator 113 will be equal to the average reference voltage value in the second circuit of the voltage comparator 113 and the logic circuit 121 sends a signal to the amplifier 123 to disconnect the thyristor 103 »by cutting electrical power to the resistance heating element 125. The thyristor 103 remains in the non-conducting state until the water temperature detected by the the temperature sensor 102 falls below the prescribed temperature by a predetermined amount »as described below. The signal voltage in the first circuit of the voltage comparator 113 and the reference voltage in the second circuit of the voltage comparator 113 must have values that allow the logic circuit 121 to produce a signal to the amplifier 123 which will properly control the thyristor 103 to heat the water at the desired temperature. The prescribed temperature device 101 is a variable resistor whose resistance can be manually adjusted to change the prescribed temperature. The temperature sensor 102 is a thermometer where the resistance decreases as the detected temperature of the water increases. The values of resistors 126 and 127 are selected such that the signal voltage at point 111 will be proportional to the difference between the prescribed temperature and the detected water temperature. The reference voltage at point 116 is determined by the value of resistors 114 and 115 »and the magnitude of the sawtooth voltage imposed on the reference voltage at point 119 is determined by the values of resistors 12B and 129. The values for these resistors should be adjusted to accommodate the characteristics of the particular prescribed temperature device 101, the temperature detector 102 and the logic chip 104 selected for the proportional band temperature control circuit 100. As described above. »The optoelectric coupler 10B is included in the proportional band temperature control circuit 100 to avoid excessive cyclic variations of the thyristor 103 when the detected water temperature is around the prescribed temperature. When the detected water temperature is equal to the prescribed temperature, the circuit 121 sends a signal to the amplifier 123 to disconnect the thyristor 103 and stop the conduction of the electric power to the resistance heating element 125. Without the opto-coupler 10T »when the temperature of the detected water drops slightly »for example» less than 1 ° C »below the prescribed temperature» the logic circuit 121 will send a signal to the amplifier 123 to open the thyristor 103 and conduct the electrical energy to the resistance heating element 125 until the detected water temperature is heated again to the prescribed temperature. This action results in the rapid on and off of the thyristor 103 »to control the detected water temperature as accurately as possible at the prescribed temperature. The opto-electrical coupler 108. electrically connected through the resistance heating element 125 by transmission lines 130 and 131 »operates in such a way that the sensed temperature simulates having approximately 5 ° C more than what it actually has when the electrical energy flows through the resistance heating element 125. In this way, when the temperature of the water detected by the temperature sensor 102 reaches the prescribed temperature »the thyristor 103 stops conducting electrical power through the resistance heating element 125 and optoelectric coupler 108. As no current flows through the opto-coupler electr. 108"the signal voltage at point 111 is determined by the voltage drop across the temperature sensor 102 and the voltage drop across the prescribed value device 101" resistor 126"and resistor 127. The resistor 127 it produces a voltage drop equivalent to the voltage drop caused by approximately a temperature change of 5 ° C at the detected temperature. Therefore, the detected temperature pretends to be about 5 ° C more than real "and the sensed temperature must fall by an additional 5 ° C before the signal voltage in the first circuit of the voltage comparator 113 indicates that the temperature is below the prescribed temperature. When the voltage comparator 113 sends a signal to the logic circuit 121 that the sensed temperature is below the prescribed temperature, the logic circuit 121 sends a signal to the amplifier 123 to open the thyristor 103 and allow the electrical energy to flow through. of the resistance heating element 125. With the electrical energy flowing through the resistance heating element 125 »the electrical energy flows through the opto-electric coupler 108 through the transmission lines 130 and 131. With the electric power which flows through the opto-electric coupler 108 »the resistor 127 deviates and the inclination of 5 ° C at the apparent detected water temperature is removed. The circuit 121 then sends a signal to the amplifier 123 to open the thyristor 103 until the temperature of the detected water reaches the prescribed temperature again. This action of the optocoupler 108 allows the sensed temperature to fall approximately 5 ° C below the prescribed temperature before the thyristor 103 again conducts electrical power through the resistive heating element 125, and allows the water temperature detected is heated to the temperature before the electrical power is cut from the resistance heating element 125. This action prevents the cyclic operation of the electrical energy through the resistance heating element 125 when the detected water temperature is at approximately the prescribed temperature. In an alternative embodiment, the temperature control circuit 100 could include a programmable real time switch wherein peak and reduced energy demand periods or vacation operation cycles could be programmed in the control cycle for the heating element. In addition »a pressure detector, a temperature detector» could be added »a detector of mineral deposits and / or a sensor to detect the presence of water. The control circuit would be programmed to disconnect power from the water heater and / or the heating element upon detection of the predetermined conditions or limits. Further. the control circuit could include means for automatically regulating the prescribed value in response to various conditions such as the amount of water used, or whether it is a period of peak or reduced energy demand.

EXAMPLE In a first example, an electric water heater with a heating element of resistance 4,500 watts was operated to heat water from 60 ° F to 120 ° F using a current of 240 volts. In a first work cycle, a commercially available bimetallic thermostat was used, as described in the introduction of this application, to detect the temperature of the water and control the electric current to the resistance heating element. In a second work cycle »the proportional band temperature control circuit was used» as shown in fig. 2 and described in this application "to detect the water temperature and control the flow of electric current to the resistance heating element. The results of the two comparative work cycles are shown in Figure 3 of the drawings. For Work Cycle 1 »the tension on a bimetallic thermostat was regulated with a threaded bolt such that the bimetallic thermostat would be placed abruptly from a flat configuration to a domed configuration at a prescribed temperature of 120 ° F. The bimetallic thermostat was placed in contact with the outer wall of the water heater water tank at a location about three inches above the electric resistance heater element. The bimetallic thermostat was connected »through an insulating rod, to an electrical switch in a transmission line supplying electrical energy to the resistance heating element. The water tank was filled with water at 60 ° F and the electrical power was connected to the transmission line by supplying the resistance heating element. The bimetallic thermostat remained in a flat position and the electrical switch was closed. Electric current was passed through the resistance heating element at a speed of 19.7 amperes for approximately 27 minutes until the water heated to approximately 122 ° F. Then the bimetallic thermostat was placed abruptly in the form of a dome, activating the switch to cut off the electric current to the resistance heating element. A graph of the temperature of the water as a function of time of this first work cycle is shown in figure 3. For Work Cycle 2, a proportional band temperature control circuit was used, as shown in the figure 2 and described above in this application. The prescribed temperature device 101 was heated to a prescribed value of 120 ° F, and the temperature sensing device of the thermistor 102 was adhered to the water tank approximately three inches above the resistance heating element 125. The thyristor 103 was connected to the resistance heating element 125. The water heater water tank was emptied and refilled with water at 60 ° F and the proportional band temperature control circuit 100 was connected to the electric power grid. The proportional band temperature control circuit 100 initially IB.8 amperes of electricity to the resistance heating element 125, ie, approximately 95% of the amperes supplied by the thermostat. Mechanical of Cycle 2B of Work 1. After approximately four minutes (at 6B ° F). the proportional band temperature control circuit 100 decreased the electricity supplied to the resistance heating element 125 to IB.6 amperes, that is to say »about 91% of the amperes supplied by the mechanical thermostat of Work Cycle 1. After approximately 21 minutes (at 104 ° F) »the temperature of the detected water entered the proportional band temperature range and the proportional band temperature control circuit 100 slowly began to reduce the electrical current to the resistance heating element 125» until after 27 minutes the temperature of the water detected reached the prescribed temperature and the circuit of Proportional band temperature 100 cut the electric current to the resistance heating element 125. Figure 3 shows that the same amount of water was heated to substantially the same temperature in the same amount of time in the Work Cycle 1 as in the Cycle Work 2. However, "in Work Cycle 1", 19.7 amperes of electricity were required and in Work Cycle 2. only about 18.6 amperes of electricity were required throughout the warm-up period. That is to say »heating water in a water heater equipped with the proportional band temperature control circuit of the present invention, which supplies electricity to the resistance heating element 125 in short discharges followed by short periods in which the electricity is cut off, requires approximately 9% less electrical energy than heating the same amount of water to the same temperature in the same heater of water »but using a mechanical temperature controller. This is an unexpected result. The pulsing of current to the load by the proportional band temperature control circuit allows the water temperature to rise and fall rapidly in small quantities in response to the applied current. A brief interruption of the current applied to the heating element each cycle allows a more efficient transfer of radiation energy to the guide from the heating element. As a second example, a test was conducted to determine the actual amount of energy that a consumer would use during a typical hot water heater operating cycle. With reference to figure 4. the real lovt-hours (kWh) are plotted as a function of time for a mechanical thermostat and an electronic thermostat including proportional band control logic. Figure 4 illustrates that during a typical heating cycle, approximately 3% less energy is used as a direct result of using the proportional band control logic. It is possible that this percentage could be increased to approximately 5-5.5% by changing the conduction angle of the triac ignition quadrants without adversely affecting the performance of the water heater. Furthermore, by limiting the current to the heating element using proportional band control logic and supplying current to the heater in pulses, gradually coasting to the prescribed temperature without exceeding the desired temperature offers an additional energy reduction of 15%. The combination of current modulation and avoidance of exceeding the prescribed temperatures offers the consumer a combined energy saving of almost 20% over the operating cost of a similar heater using a bi-lateral mechanical thermostat. Overheating the water by passing a reasonable temperature of 125 ° F-130 ° F generally wastes energy. A typical two-inch-thick insulation layer loses its ability to effectively retain heat at temperatures roughly above 130 ° F. This loss of energy in reserve operation mode is not profitable and leads to potentially heater cicle more than necessary. The proportional band control circuit of the present invention avoids excessive responses and allows the water temperature to fall only a little more or less 5 ° F to cycle only the difference necessary to return the water temperature to a desired prescribed value.

An additional advantage of the proportional band control circuit is its appropriateness for a flammable vapor environment. For example, »such a medium can exist in a garage» a workshop »or storage area in a basement where there can be» gasoline »propane or other highly flammable or explosive vapors. Mechanical thermostats and contact type switching devices may present a discharge of electricity when an electrical contact is made or broken »depending on the amount of switched current. The electric arc can ignite a flammable vapor if the steam is sufficiently volatile. On the contrary »the proportional band control circuit is a totally solid state» does not have moving parts, and would not ignite flammable. Although a particular embodiment of the invention has been shown and described in this document, changes and modifications can be made without departing from the spirit and scope of the invention. For example, logic chips can be used in addition to the Motorola UAA1016A logic chip to control the cycle of connection and disconnection of the thyristor 103. Furthermore, a temperature sensing device can be used in addition to the thermistor used as a temperature sensing device 102. It is also possible to You can use thyristor 103 as a thyristor that is not a Motorola TRIAC. Therefore, no limitations of the invention are proposed except for the limitations found in the appendix.

Claims (17)

NOVELTY OF THE INVENTION CLAIMS

1. - For a water heater comprising a water tank and an electrical resistance heater element that extends into the water tank »an improved method for heating water in the water tank from an initial cold temperature to a warmer prescribed temperature pre-selected »said method comprises: conducting electrical energy to the electrical resistance heating element in discharges» each discharge of electrical energy followed by a period during which electrical energy is not conducted through the electric resistance heating element. 2 .- The method of the re vind cac ón 1 »where the electricity supplied to the electric resistance heating element is alternating current; wherein the period of each electric power discharge is a fraction of each cycle of alternating current; and wherein the period following each discharge of electrical energy, during which electrical power is not conducted through the electrical resistance heating element, comprises the remaining fraction of each cycle of alternating current. 3. The method of claim 2 wherein the period of each electric power discharge is about 95% or less of each cycle of alternating current. 4.- In a water heater comprising a water tank »having an external wall, to contain water and an electrical resistance heating element that extends inside the water tank to heat the water in the tank» the improvement comprises : a temperature controller to conduct electric power to the electric resistance heating element to heat the water in the water tank »said temperature controller conducts electrical energy to the electric resistance heating element in discharges, each discharge followed by a period during which electrical energy is not conducted to the electrical resistance heating element »to improve the efficiency of heating the water in the water tank. 5. The water heater of claim 4 wherein: the temperature controller comprises: a logic circuit for limiting a cycle "comprising a discharge of electrical energy and the period that follows during which electric power is not conducted" to approximately one second or less, and to limit each discharge of electrical energy to no more than 95% of each cycle. 6. The water heater of claim 5. wherein the temperature controller comprises: a temperature device prescribed to establish the prescribed temperature up to which the temperature controller will heat the water in the water tank; a temperature sensing device that detects the temperature of the water in the water tank; differential temperature means in the logic circuit to determine the temperature difference between the detected water temperature and the prescribed temperature; and means in the logic circuit for stopping the conduction of electrical energy to the heating element of electrical resistance when the detected temperature is at or above the prescribed temperature. 7. The water heater of the rei indication 6 where the temperature controller is a proportional band temperature controller and includes: a proportional band device which. as the detected temperature approaches within a selected proportional band margin at the prescribed temperature, it cycles to the temperature controller from a line where the temperature controller can conduct electrical energy to the electric resistance heating element to a condition where the temperature controller can not conduct electrical energy to the electric resistance heater element »each cycle has a period of about one second or less and the proportion of each cycle period during which the temperature controller can conduct electric power decreases as the temperature detected. when it is in the proportional band margin, it is closer to the prescribed temperature. 8. The water heater of claim 7, wherein the temperature controller includes: an anti-cycling operating device which "once the temperature reaches the prescribed temperature" fixed to the temperature controller in a condition of no-driving until the detected temperature drops to a differential selected from the prescribed temperature. 9.- A water heater »comprising: a permanent water tank closed to contain water; a water inlet duct to add cold water to the water tank a water outlet duct to remove heated water from the water tank; an electric resistance heating element that extends inside the water tank to heat water in the water tank; and a control circuit for conducting electrical energy to the electric resistance heating element in discharges, each discharge followed by a period during which no electric power is conducted to the electric resistance heating element, thereby improving the efficiency of heating the water in the water tank. 10. The water heater as recited in claim 9, wherein the tank has a lid and a bottom, and wherein the water inlet conduit includes a dip tube that extends into the tank in a tank. point adjacent to the top of the tank and that has an outlet adjacent to the bottom of the tank. 11. The water heater as recited in claim 10, wherein the water outlet conduit has an inlet adjacent to the tank top. 1

2. The water heater as recited in claim 9 and further comprising a frame surrounding the tank to define a space between the tank and the frame and insulation within the space. 1

3. The water heater as recited in claim 9 »wherein a discharge of electrical energy and the period that follows during which no electric power is conducted define a cycle, the control circuit limiting the cycle to approximately one second or less. 1

4. The water heater as recited in claim 13 »wherein the control circuit limits the discharge to less than about 96% of each cycle. 1

5. The water heater as recited in claim 13, wherein the control circuit includes a temperature device prescribed to establish a prescribed temperature at which the control circuit will heat the water in the water tank. temperature detector that detects a detected temperature of the water in the water tank, and a logic circuit to determine the temperature differential between the water temperature detected and the prescribed temperature and to stop the conduction of energy to the electric resistance heating element when At the detected temperature it is at or above the prescribed temperature. 1

6. The water heater as recited in claim 15, wherein the logic circuit is a proportional band temperature controller "where" when the detected temperature is within a predetermined proportional band margin. The duration of each discharge decreases as the detected temperature approaches the prescribed temperature. 17.- The water heater as mentioned in the re indication 16 »where the control circuit includes means to avoid excessive cyclic variations of the logic circuit» such that when the detected temperature reaches the prescribed temperature the energy conduction to the element The electric resistance heater is stopped until the detected temperature falls below the prescribed temperature by a predetermined amount. IB.- The water heater as recited in claim 1

7. wherein the means for preventing excessive cyclical variations includes an optoelectric coupler. 19. The water heater as cited in claim 18, wherein the opto-electric coupler conducts current when energy is conducted to the electric resistance heater element. 20. The water heater as recited in claim 17, wherein the means for preventing excessive cyclical operation operates to make the sensed temperature simulate in front of the logic circuit to be higher than the actual by the predetermined amount. 21.- A water heater, comprising: a permanently closed water tank to hold water »a water inlet duct to add cold water to the water tank, a water outlet duct to remove water from the water tank, in an electric resistance heater element that extends inside the tank to heat water in the tank »a control circuit to conduct electrical energy to the electric resistance heater element in discharges »Each discharge followed by a period during which electrical power is not conducted to the electric resistance heating element, where a discharge of electrical energy and the period that follows during which no electrical power is conducted define a periodic cycle» a device of prescribed temperature to establish the prescribed temperature at which the control circuit will heat the water in the water tank, a temperature detector that detects the water temperature in the water tank, and a proportional band temperature controller that includes a logic circuit to determine the temperature differential between the water temperature detected and the prescribed temperature and to stop the conduction of energy to the heating element of electrical resistance when the detected temperature is at or above the prescribed temperature. 22. The water heater as recited in claim 21, wherein the duration of each discharge decreases as the detected temperature approaches the prescribed temperature when the detected temperature falls within a range of the predetermined proportional band. 23. The water heater as cited in claim 21, further includes a programmable real time switch to program peak and reduced water usage times where the prescribed temperature is regulated in response to the use of the water. 24. The water heater as recited in claim 21, further includes means for detecting the use of water and wherein the prescribed temperature is regulated when the use of the water is below a predetermined amount. 25. The water heater as recited in claim 21. further includes a pressure sensor and wherein the energy is disconnected from the water heater when a predetermined pressure is reached. 26. The water heater as recited in claim 21, wherein the energy is disconnected from the water heater when a predetermined water temperature is reached. 27. The water heater as recited in claim 21 further includes means for detecting the presence of water and where the controller becomes inoperative when there is no water in the tank. 2B.- The water heater as recited in claim 21 »further includes an operator interface for operating the controller and having secured access. 29. The water heater as recited in claim 28, wherein the operator interface can be accessed by remote control. 30. The water heater as cited in claim 28, wherein the operator interface includes a visual indication of the operation of the controller including malfunctions. 31. The water heater as recited in claim 21 further includes a plurality of temperature detectors for detecting the temperature of the water in a plurality of locations in the water tank and where the controller is sensitive to water. the plurality of temperature detectors.