Instantaneous water heater system

Abstract

A continuous flow heater system (100) with a heat exchanger device (20) comprising at least one hollow chamber (21, 22, 23, 24) and at least one electrical heating element (52, 53, 54), further comprising at least:- a control device (30) with a temperature control unit (35), a withdrawal counter unit (32), a standstill counter unit (33) and a time delay unit (34);- an electrical switching element (41, 42, 43) for connecting and disconnecting one or more heating elements (52, 53, 54) from / to the power supply;- an outlet temperature sensor (27) connected to the temperature control unit (35);- a flow sensor (29); wherein:- the withdrawal counter unit (32) is connected to the flow sensor (29) and is designed to be triggered when the water flow rate exceeds a withdrawal threshold value V̇0;- the standstill counter unit (33) is designed to be triggered and retriggered by the withdrawal counter unit (32), and both are designed to deliver a standstill event signal after a period of inactivity without water flow and to record the duration of inactivity;- the time delay unit (34) is connected to the withdrawal counter unit (32) and is designed to be triggered thereby and to start a delay time ΔtOFF, the duration of which is switched from a short standard delay time to a long delay time by the standstill signal provided by the standstill counter unit (33); and- the switching elements (41, 42, 43) are designed to be triggered by the time delay unit (34) only after the delay time has elapsed.

Description

FIELD OF THE INVENTIONThe present invention relates to a continuous flow heater system, and more particularly to a continuous flow heater system for a body emergency shower.BACKGROUND OF THE INVENTIONContinuous flow heaters immediately supply warm or even hot water on demand. After opening a valve or tap, the water is heated as it flows through the water heating system. The heating is effected with the aid of one or more electrical heating element(s) which project into the path of the water. The temperature increase which the heater can generate at a specific water flow rate is limited by the defined heat capacity of the water heater. Since only one electric heating element or a small number of electric heating elements are required for these purposes, the so-called storage mass, i.e. the heat storage capacity, is low in these systems.However, there are special applications where a large hot water flow rate must be provided quickly, for example, in emergency body showers. Emergency body showers with large flow rates and multiple shower heads that trigger a surge of water serve for the rapid cleaning of persons contaminated with hazardous substances, such as acids or alkalis used in the chemical industry. To promptly provide such a large flow rate of hot water for purging with an appropriate temperature rise, sufficient electric power is required to simultaneously operate a row or a pair of electric heating elements. As long as the water flows, the heating process and the temperature control process are easy to handle when sufficient electric power is installed. The required electrical power can be automatically adapted to the water throughput and / or the required temperature rise and is also constantly monitored by an outlet temperature sensor.For a series of successive withdrawals, an undesirable temperature rise may occur, which increases the risk of scalding. These problems are exacerbated when this occurs frequently and the inactivity time is shorter than the sampling time. During the shutdown period, the stagnant residual water continues to heat by the latent heat stored in the large storage mass of the heating elements and the stainless steel chambers in which they are mounted, even when the power supply is interrupted. When water is removed again, the hot residual water flows out of the device and can represent an enormous risk of brewing for the user. The temperature rise caused by the latent heat energy cannot be controlled by the temperature control unit of the water heating system in any way. The latent heat problem is further exacerbated when elements of coated copper or stainless steel are used to heat the water.SUMMARY AND OBJECTS OF THE INVENTIONAccording to a preferred embodiment of the invention, there is provided a continuous heater system with heat exchanger apparatus comprising at least one hollow chamber and at least one heating element, further comprising at least:a control apparatus comprising a temperature control unit, a withdrawal operation counter unit, a standstill counter unit and a time delay unit;an electrical switching element for connecting or disconnecting one or more heating elements from / to the power supply;an output temperature sensor connected to the temperature control unit; anda flow sensor.A primary object of the invention is to provide a continuous flow heater system which avoids any scalding risks and is suitable for use in special applications such as emergency showers or emergency body showers which require the prompt and repeated provision of a large flow rate of hot water.This object is achieved by an improved control apparatus comprising a temperature control unit, a withdrawal counter unit, a standstill counter unit and a time delay unit, wherein:the extraction process counter unit is connected to the flow sensor and is triggered as soon as the water flow exceeds an extraction threshold value;the stall counter unit is retriggered by the bleed counter unit, and both provide a stall event signal after an inactivity time without water flow and detect the inactivity duration;the time delay unit is connected to the extraction process counter unit and is triggered by the latter and starts a delay time whose duration varies between a short standard delay time and a long delay time according to the determination by the stall signal provided by the stall counter unit;the start of the heating process is only triggered by the time delay unit after the delay time has elapsed.The main effect of the invention is based on a preventive temperature control which prevents an excessively high water temperature at the water outlet by taking into account the amount of potential latent heat stored in the storage mass of the heating elements and / or the chamber walls of the heat exchanger device and the period of time in which the latent heat energy can be transferred to the residual water in the device by activation of the heating elements in a new extraction cycle before the restart of the heating process. For this reason, a time delay unit is integrated into the control device in order to switch on the heating elements only after a certain delay time has elapsed. The delay time is considered to be a kind of safety period starting from the beginning of the sampling cycle in order to prevent scalding.In order to take into account the user behavior with respect to the number and duration of the taps or the duration of the interruptions between taps, a tap-process counter unit is also integrated into the control device. The extraction operation counter unit detects the duration of inactivity from the previous stop of extraction and / or the number of interruptions in a preset monitoring period. If any of these values exceeds a certain threshold value, a stall signal is sent to the time delay unit to lengthen or shorten the time delay period. Thus, a variable time function is implemented in the continuous heater system of the invention.In another embodiment, an additional water inlet temperature sensor is arranged upstream in the vicinity of the water inlet opening, and the control device further comprises a heat calculation unit. The heat computation unit has four main inputs:the inlet water temperature,the outlet water temperature,the throughput andthe duration of the extraction interval.Based on the temperature difference between the inlet and outlet temperature and the flow signal, the heat / energy required to heat the water stream in a specific time interval to a desired set outlet temperature can be calculated. The corresponding time interval is defined by the beginning and the end of the extraction process. There is also a connection from the heat calculation unit to the temperature control unit to sum the electrical energy acting on the heating elements in the same time interval. Knowing a) the amount of energy actually consumed to heat the water and b) the amount of electrical energy interacting with the heating elements, the latent heat energy, i.e. the amount of energy stored in the storage mass of the system, can be calculated. On the basis of the water temperature of the residual water at the end of the heating process and the residual water quantity in the heat exchanger device, a forecast for the development of the outlet water temperature at the beginning of the next extraction cycle can be calculated.In order to achieve an even more accurate result of the temperature rise due to the calculated latent heat, a heat loss rate can be determined experimentally and taken into account in the calculations in a further improved embodiment of the invention.In a further embodiment of the continuous flow heater system of the invention, a safety valve and a bypass are connected to the outlet. Only when the temperature at the outlet is below a safety threshold T max is the valve opened to let water into the subsequent user-contact devices, such as shower heads. Otherwise, the water is conducted via a bypass to a storage container or an outflow.Another object is to provide a method of operating a continuous flow heater system, at least comprisinga heat exchanger device having a hollow chamber and at least one electrical heating element, an output temperature sensor and a flow sensor;a control device andan electrical switching element for connecting or disconnecting the heating element from / to the power supply;The object of the invention is achieved by a method comprising the following steps:checking the user behavior by monitoring the flow rate V flow 0 with a flow sensor and checking the water temperature T by monitoring the outlet water temperature sensor in order to see whether the water flow rate exceeds a removal threshold value and the water temperature is below a setpoint temperature T 1 ;testing the heat exchanger temperature by utilizing the output temperature sensor information to set a delay time to a short standard delay time when a cold heat exchanger temperature is detected;if the heat exchanger is cold, then checking the system for a previous inactivity period Δt OFF, in which the current is interrupted and no heating takes place; resetting the delay time to the short standard delay time Δt if inactivity period Δt OFF is longer than a preset downtime value or extending the long delay time Δt for each case of inactivity;heating the water in the heat exchanger device by switching on the heating element after the delay time Δt has elapsed; andconducting the heating of water with continuous temperature control until the current is interrupted.BRIEF DESCRIPTION OF THE DRAWINGSThese and other objects of the invention will be apparent and understood by those skilled in the art from the detailed description of the preferred embodiments of the invention and the following drawings, wherein: FIG. 1 is a schematic illustration of a continuous flow heater system; FIG. 2 is a schematic illustration of a control apparatus; FIG. 3 is a flow chart of the software running in the control device; and FIG. 4 shows a plurality of diagrams of parameters over a common timeline.DETAILED DESCRIPTION OF A PREFERRED EMBODIMENTReferring now to the drawings, wherein like numerals designate like or corresponding elements throughout the several views, it will be seen that the invention relates to a continuous flow heater system 100 as schematically shown in FIG. 1.The basic components of the continuous flow heater system 100 are a heat exchanger apparatus 20 and a control apparatus 30, which components may be physically located in a common housing, but the heat exchanger apparatus 20 may also be operated by a control apparatus 30 mounted at a remote location, the heat exchanger apparatus 20 and the control apparatus 30 being connected via cables and / or wireless connections.In the illustrated embodiment of the invention, the heat exchanger apparatus 20 is comprised of a series of welded stainless steel heating tubes 21, 22, 23, 24, wherein the water flows through openings at the beginning and at the end of each tube to form a tortuous water flow path between an inlet opening at the bottom of tube 21 and an outlet opening at the top of tube 24. To clarify, in FIG. 1, only four tubes 21, 22, 23, 24 are shown for explaining the invention, whereas a genuine embodiment of a heat exchanger comprises a stack of more than one dozen chambers, in each of which an electric heating element is arranged.The heat exchanger device 20 has a connection pad 26 to be connected to a polyphase power supply. An inlet temperature sensor 28 and a flow sensor 29 are arranged in the inlet opening, and an outlet temperature sensor 27 is arranged at an outlet opening of the heat exchanger device 20. Each steel heating tube 21, 22, 23, 24 has at least one electric heating element 52, 53, 54. The switching elements 41, 42, 43 are triacs, all of which are arranged in the lowermost steel pipe 21, so that they can be cooled by the cold water flowing into the flow path there.The electronic control device 30 with a microprocessor controls the pulse frequency of the triac arrangement for controlling the heat emission of each heating element 52, 53, 54 In addition, the control device 30 receives data and / or other signals from the outlet temperature sensor 27, the inlet temperature sensor 28 and the flow sensor 29 It also has a user interface 36.The internal structure of the control device 30 is shown in more detail in the schematic illustration in FIG. 2. It is controlled by a microprocessor 31 and has a software program for controlling the activation and deactivation of the heating elements 52, 53, 54 and the outlet temperature to a temperature close to the desired set point. The set point information is provided by the controller 30 via the user interface 36 with a display and buttons and / or buttons for adjustment operations such as selection of the desired temperature set point.The control device 30 comprises a plurality of units:a temperature control unit 35,a sample counter unit 32,a standstill counter unit 33; anda time delay unit 34.With respect to a software program, they are integrated as modules, routines and / or subroutines. With respect to the hardware, they are integrated packages or units connected to each other by a data bus, for example.The sampling counter unit 32 is connected to the flow sensor 29 and the outlet temperature sensor 27. It is triggered when the water flow rate V exceeds a removal threshold value Vegr 1 and the outlet water temperature is below a temperature setpoint value T 1.The stall counter unit 33 is retriggered by the bleed counter unit 32 each time the bleed is interrupted and provides a stall signal after an inactivity period without water flow.The time delay unit 34 is connected to the extraction counter unit 32, is triggered by the latter and starts a delay time t 1, the duration of which is switched from a short standard delay time to a long delay time by the stall signal provided by the stall counter unit 33.The switching elements 41, 42, 43 are likewise connected to the regulating device 30. Depending on the outlet water temperature at the outlet temperature sensor 27, one or more switching elements 41, 42, 43 are triggered in order to switch on the number of electrical heating elements 52, 53, 54 required for heating the water to the desired outlet temperature. The switching elements 41, 42, 43 can be activated only after the expiration of the delay time. The delay time is set by the time delay unit 34.The software in the control device 30 comprises a method of the invention for operating a continuous-flow heater system without risk of scalding due to latent heating effects of the thermal masses.The method will be described in detail with reference to the flow chart in FIG. 3 :A start block 201 of the control process 200 runs in the control device 30, which is also an end point in an endless loop or a rolling control process.The signal or data provided by the flow sensor 29 is monitored and adjusted at decision block 202 to a minimum flow preset as the sampling threshold Vba 1 whereby the control process begins again at block 201. The measured throughput value V is below the removal threshold value Vef 1, if no water flows or only water drips.Once the throughput V is above the threshold Vef 1 detected in decision block 202, a temperature comparison routine 203 is executed. A comparison is made with the user-selected temperature set point T 1. If the measured current water temperature T is above the selected T 1 then no heating is required and the control process begins again at block 201. If the current temperature T is below the setpoint temperature T 1 then the next temperature comparison is made in block 204 where the heat exchanger temperature is evaluated using the temperature information from the outlet temperature sensor. The temperature indication T is input in decision block 204.If the heat exchanger apparatus 20 is cold, a short delay time is selected in the time delay unit 34 in decision block 204. A preferred feature of the invention is that a short delay time of at least 1 second is always fixed. This short delay is useful for venting the system. Any air layer, whether so thin, would isolate the metal surface of the heating elements from the fluid, creating the risk of overheating the heating elements because heat transfer into the water through the air layer would be at least partially prevented.After the delay time has elapsed, the heating process may start at block 208 controlled by the temperature control unit 35 to bring the outlet water temperature close to the set point T 0. The heating is effected either constantly by adapting the electrical output power for all heating elements together or by heating at a plurality of short time intervals with constant power. A third adjustment option can be selected, in which only a part of the plurality of heating elements provided in the device is selectively switched on.The heating process is ended when the water flow is interrupted or when the water temperature T is close to the preset temperature value T 0. If either of these conditions is met, the heating process is interrupted at block 208 and the monitoring process is restarted at block 201.If, on the other hand, it is determined in decision block 204 that the heat exchanger device 20 is still hot, then the next condition is evaluated in decision block 205. If the standstill counter unit 33 detects a standstill event, the delay time is extended considerably to a long delay time, which can initially take 5 seconds, for example. The exact value depends on the design of the heat exchanger device 20, the number of heating elements 52, 53, 54, the insulation properties, etc. It is always preset to ensure that the water temperature cannot increase beyond a safety temperature threshold by the latent heat energy.The connection of the temperature control unit 35, the stall counter unit 33 and the time delay unit 34 is an important feature because all the elements interactively judge whether or not heating is started by turning on at least one heating element. The standstill counter unit 33 is used to regulate a temperature rise by means of a controllable timer function, wherein the standstill time depends on the number of successive withdrawal processes, which is followed in each case by an inactive period.In the process example illustrated in the flowchart in FIG. 3, the temperature target value T 1 is set to 100° F. A heating downtime is defined as t OFF= 5 min.If the value of the outlet temperature sensor 27 is more than 100° F., the status of the heat exchanger device 20 is deemed to be "hot" in block 204, otherwise it is "cold".If the status is "cold", the delay time is set to the short time, such as 1 second, regardless of whether there are successive short taps or activation taps.If the status is "hot", the delay time calculated by the time delay unit 34 begins to become longer for each successive activation after a heat-up shutdown of less than t OFF= 5 min. The stall t OFF is detected by the stall counter unit 33. Only when the standstill time exceeds t OFF is the delay time reset to 1 second.When a standstill occurs for the first time, the delay time is set to 5 seconds. At the second entry, it is 10 seconds and at the third, 15 seconds. The delay time is set in block 206.At any further entry, the delay time remains at 15 seconds until a complete inactivity period of at least 5 minutes is reached. After this inactivity period, the delay time is reset to 5 seconds.The operation of the continuous heater system 100 of the invention and the method of operation will be described in detail with reference to FIG. 4. FIG. 4 shows five diagrams over a common time strip t for:- Flow rate V measured by flow sensor 29,water outlet temperature T, measured by outlet temperature sensor 27,electrical power P acting on the heating elements 52, 53, 54,time delay Δt and- Stall event counter n OFF.When the operation of the continuous heater system 100 starts at t=0, no flow is indicated, so that V=0. At the beginning of a discharging operation, the water temperature T 0 may be the ambient temperature or lower when the system is turned on, or the temperature of the previous heating operation. In FIG. 4, the water temperature T corresponds to the cold water temperature, which is approximately T 0= 50 °... 60° F. Since no throughput is indicated, none of the heating elements 52, 53, 54 is active, so the electrical power P=0. The time delay Δt is set to a default value for a short delay time, which is Δt=1 s. No stall event has yet occurred, so the stall counter n is OFF= 0.At t 1 the user opens the valve or tap, but only slightly. A throughput is detected, but V is still below a sampling threshold Vegr 0. Therefore, the monitoring routine in the software of the controller returns from decision block 202 to begin at block 201 (see FIG. 3 ). Water temperature T, electric power P, delay time Δt and standstill event n OFF all remain unchanged.At t 2 the throughput V is above the extraction threshold value Vef 0. In addition, the water temperature T is significantly below the user preset temperature T 1, and therefore the maximum power electric power P is turned on, i.e., all available heating elements 52, 53, 54 are turned on after a very short delay time Δt of 1 s set to remove air contaminants from the surface of the heating elements. Consequently, the water temperature T rises. Before the setpoint value T 1 is reached, the electrical power P is reduced by switching off a single heating element on further heating with the remaining number of heating elements. As the temperature approaches the set point T 1 further heating elements are turned off.At t 3 the flow is interrupted by the user causing:The water temperature T continues to rise due to the latent heat energy in the system, but since the electric power P has already been reduced before the interruption, the latent heat energy is limited. Thus, the water temperature T continues to remain below a safety threshold T max.A first standstill event is detected in the extraction counter unit 32, therefore n OFF= 1.With n OFF= 1 the time delay unit 34 is triggered, whereby the delay time is set to the default value for a long delay time, namely Δt=5 s.At t 4, only a very short time after the interruption beginning with t 3 the user starts to remove again, so that V again lies above the removal threshold value Vadd 0. The heat exchanger device 20 cools down as a result of the incoming fresh water, so that the outlet temperature T decreases, but on account of the delay time Δt set at t 3 to 5 s, the full electrical power for all heating elements is switched on after the end of the standstill time t 5 of 5 s. The left hatched area in the graph for the power P shows the amount of energy which has not yet been made available for heating up the system due to the delay time. Otherwise, the water temperature rises above the safety threshold value T max, which represents a risk of brewing. Due to the delay time Δt applied, the entire system is first rinsed with cold water before the temperature control is carried out again.At t 6 the user interrupts the flow again for a very short time until t 7. Due to the interruption, the stall counter is set to n OFF= 2 and the delay time is extended by another 5 sec to Δt=10 sec in total. The delay time Δt starts at t 7, when the extraction is resumed. However, the flow interruption between t 6 and t 7 was even shorter than the delay time Δt=10 s, so that no electric power P was provided at all during this time. The shaded area again corresponds to the amount of electrical energy that would have been provided to the system if the water extraction and the switching on of the heating elements were carried out simultaneously as in the prior art. The broken line in the temperature diagram shows how the water temperature T may increase when the current is immediately turned on with the resumption of the extraction process. The continuous temperature line, on the other hand, shows that the temperature decreases in the heat exchanger system of the invention.At t 8 the delay time Δt still continued when the flow is interrupted again, thus a further standstill event is detected in the extraction counter unit 32 and n OFF is set to 3, which corresponds to the maximum value in the example process under consideration here. The delay time is extended by a further 5 s to Δt=15 s, which likewise corresponds to the maximum for this value.Whenever an interruption of the water flow is detected, the stall counter for stall events is set to a new value and the detection of the stall time t OFF is restarted. In the previous period between the starting point of the process at t=0 and t 8 the complete downtime of 5 minutes was never reached. However, a 5-minute period that has started at t 8 ends at t 9. At t 9 the stall counter is reset to zero and the delay time is reset to the default value of 1 sec.Thus, at t 9 the system is reset to the state in which it was at the very beginning of the described process. No provision is required because no latent heat problem may occur in this state. Once a purging operation begins, for example at t 10, heating starts almost immediately after the minimum delay time of Δt=1 second, which serves to purge trapped air from the system before the start of heating.

Claims

A continuous flow heater system (100) having a heat exchanger device (20) comprising at least one hollow chamber (21, 22, 23, 24) and at least one electric heating element (52, 53, 54), further comprising at least: - a control device (30) having a temperature control unit (35), a withdrawal counter unit (32), a standstill counter unit (33) and a time delay unit (34); - an electric switching element (41, 42, 43) for connecting and disconnecting one or more heating elements (52, 53, 54) from / to the power supply; - an outlet temperature sensor (27) connected to the temperature control unit (35); - a flow sensor (29); wherein: - the withdrawal counter unit (32) is connected to the flow sensor (29) and is configured to be triggered when the water flow rate exceeds a withdrawal threshold value Vegr 0 ; the standstill counter unit (33) is designed to be triggered and retriggered by the removal counter unit (32), and both are designed to supply a standstill event signal after an inactivity time without water flow and to detect the inactivity duration; the time delay unit (34) is connected to the removal counter unit (32) and is designed to be triggered by the latter and to start a delay time Δt OFF whose duration is switched from a short standard delay time to a long delay time by the standstill signal provided by the standstill counter unit (33); and the switching elements (41, 42, 43) are designed to be triggered by the time delay unit (34) only after the delay time has elapsed.The continuous flow heater system of claim 1, wherein the long delay time is increased by each stall signal provided by the stall counter unit (33) until a maximum delay time is reached.The continuous flow heater system (100) of claim 2, wherein the control device (30) comprises a microprocessor (31) and a memory, and wherein all units (32, 33, 34, 35) are implemented in a software program running in the control device (30).The continuous flow heater system (100) of claim 3, wherein an inlet temperature sensor (28) is disposed proximate the water inlet port, and the controller (30) further comprises a thermal computation unit.The continuous flow heater system (100) of claim 1, wherein the switching elements (41, 42, 43) are triacs arranged in one or more upstream hollow chambers (21) of the heat exchanger device (20).The continuous flow heater system (100) of claim 5, wherein a plurality of hollow chambers (21, 22, 23, 24) are interconnected to form a fluid flow path from an inlet orifice (24) through the hollow chambers (21, 22, 23, 24) to an outlet orifice (25).The continuous flow heater system (100) of claim 6, wherein a heating element (52, 53, 54) is disposed in each hollow chamber (22, 23, 24), except for the lowermost hollow chamber (21) in which the triacs are located.The continuous flow heater system (100) of claim 7, wherein the hollow chambers (21, 22, 23, 24) are rectangular steel tubes arranged one above the other in a single row or multiple rows, wherein the inlet opening is arranged at the bottom of the stack and the outlet opening is arranged at the top of the stack.Method for operating a continuous heater system (100), at least comprising - a heat exchanger device (20) having a hollow chamber (21, 22, 23, 24) and at least one electric heating element (52, 53, 54), an outlet temperature sensor (27) and a flow sensor (29); - a regulating device (30) and - an electric switching element (41, 42, 43) for connecting and disconnecting the heating element (52, 53, 54) from / to the power supply; the method comprising: - checking whether water flows by monitoring the flow rate V with the flow sensor (29) and checking the water temperature T by monitoring the outlet temperature sensor (27) in order to see whether the water flow rate V is above a removal threshold value Vshift 0 and the water temperature T is below a setpoint temperature T 1; checking the temperature of the heat exchanger device (20) by using the temperature indication from the outlet temperature sensor (27) with setting a delay time Δt to a short standard delay time when the heat exchanger is cold; - if the heat exchanger device (20) is cold, then checking the system for a previous inactivity period Δt OFF, in which the current is interrupted and no heating takes place; resetting the delay time Δt to the short standard delay time Δt if inactivity period Δt OFF has continued for longer than a preset downtime value or setting a long delay time Δt which is extended for each case of inactivity; heating the water in the heat exchanger device (20) by activation of at least one of the heating elements (52, 53, 54) after the delay time Δt has elapsed, and carrying out the water heating with continuous temperature control until the current is interrupted.The method of claim 9, wherein the short default delay time is at least Δt = 1 s.The method of claim 10, wherein the long delay time is set to at least Δt = 5 s.The method of claim 11, wherein the long delay time Δt is increased by 5 s for each case of inactivity.The method of claim 12, wherein the inactivity time Δt OFF is set to at least 5 minutes.

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