WO1999040375A1

WO1999040375A1 - Instantaneous fluid heating device and process

Info

Publication number: WO1999040375A1
Application number: PCT/US1999/002403
Authority: WO
Inventors: Robert W. Mann; Herman H. Hall, Jr.
Original assignee: Mann Robert W; Hall Herman H Jr
Priority date: 1998-02-09
Filing date: 1999-02-04
Publication date: 1999-08-12

Abstract

The subject invention pertains to a method and device for supplying a continuous stream of a heated fluid on demand. Preferably, a selectable fluid set point temperature is maintained regardless of changes in process dynamics, at essentially all times across a wide range of process dynamics that are determined by an application. This invention can incorporate an electrically powered heating source and utilize an electronic temperature control device. In addition, optional internal fluid recirculation, optional indirect temperature regulation, and optional flow augmentation can also be utilized with the subject invention.

Description

1 DESCRIPTION

INSTANTANEOUS FLiπD HEATING DEVICE AND PROCESS

Field of Invention

The apparatus and process taught herein relate generally to the field of fluid heating devices, including those adapted for the provision of heated water. More specifically, they relate to the provision of those types of fluid heaters that are typically referred to as "tankless," "instantaneous," and/or "on demand." The subject invention also pertains to chemical processing, processing of slurries and molten material.

Background of the Invention Prior Art in the Field

Fluid heating devices may be divided into two broad categories, (i) those which store heated fluid (tank, storage, heated fluid belt, etc.) and hereinafter referred to as Storage

Device(s)) or Storage System(s), and, (ii) those which rely on heating of a fluid while the fluid passes through the device (instantaneous, on demand, etc) and hereinafter referred to as

Instantaneous Device(s) or Instantaneous System(s).

With regard to Storage Devices and Instantaneous Devices, these may be characterized by two modes of basic operation; (i) an operational mode wherein fluid is stored during periods where there is no demand for heated fluid, hereinafter referred to as a period of Idle Use, and,

(ii), an operational mode wherein heated fluid is discharged for use within an application, hereinafter referred to as a period of Active Use.

The storage type of fluid heater is by far the more common in most applications and relies on thermostatically controlled heating element(s) to bring a reservoir of fluid in a storage tank to the desired ("set point") temperature for use. It is still the unit of choice for most household and commercial uses. However, as outlined below, its shortcomings have led to attempts to develop instantaneous fluid heaters that do not utilize a storage tank, but instead rely on the heating of fluid only as demanded. These types of systems have also had numerous drawbacks, as hereinafter described.

With regard to periods of Idle Use, Storage Devices typically store preheated fluid where the preheated fluid is available in advance of Active Use periods, and is common in the art. Such Storage Devices typically require time to recover after periods of Active Use in order to pre-heat and store a fluid during periods of Idle Use, so that heated fluid is once again available during periods of Active Use, and is hereinafter referred to as the Recovery Period. Instantaneous Devices do not typically store pre-heated fluid during periods of Idle Use, and such Instantaneous Devices are powerful enough to quickly heat a fluid to a desired temperature as a fluid passes through the Instantaneous Device and in response to a demand for heated fluid during Active Use periods up to the rated power of such an Instantaneous Device, and is hereinafter referred to as Warmup Time. Therefore, the period of Idle Use and the decided approach to storing heated fluid or unheated fluid is essentially determined by the internal fluid capacity of the device and the power of the device in order to achieve acceptable Recovery Times and Warmup Times.

The ability of a fluid heating device to precisely regulate a selectable set point temperature is impacted by physical anomalies such as the specific heat of a fluid being heated, the discharge rate of heated fluid from the fluid heating device, the temperature of a fluid to be heated entering the device, and other variables hereinafter referred to as the Process Dynamics, or, the Dynamic Characteristics of the application. The electronic temperature control devices known in the art are commonly referred to as thermostatic, on/off, proportional, proportioning, PI, PID, Fuzzy logic, Artificial intelligence, Staged, and numerous other types well known in the art and obvious upon review and hereinafter referred to as Common Temperature Control Devices. Storage type fluid or water heaters are typically beset by numerous difficulties that are well known in the art. First, only a limited amount of heated fluid is available, as determined by the capacity for the storage tank. Storage devices typically require a recovery period after a period of active use. In fact, there can be situations where the amount of heated fluid in storage is totally consumed. It also may result in an extended period wherein the unheated fluid in the storage tank is being brought back to the set point temperature and heated fluid is, therefore, unavailable to the user. Second, energy is wasted due to the necessity of maintaining the temperature of the heated fluid in storage when it is not in use (i.e., "standby loss"). Standby loss is exacerbated by the large size of the tank necessary to store heated fluid in reasonable amounts for the user and the heat loss from the large surface areas of such tanks. Third, systems of this type often accumulate a layer of sediment in the bottom of the storage tank. Such sediment may cover the heating element(s), resulting in decreased efficiency in heating the fluid in the tank. This, in turn, requires more extended operation of the heating element(s) in order to bring the fluid in the storage tank to the set point temperature with consequent increases in energy consumption/cost and a decrease in the useful life of the heating element(s) utilized.

Fourth, systems of this type often have a shortened tank life due to the accumulation of sediment in the tank, and accelerated galvanic action and electrolysis that results from the constant storage of heated fluid within the tank. Fifth, as heated fluid is drawn by the user, incoming cold fluid decreases the temperature of the remaining fluid in storage. This results in a need for continual adjustment of the balance of hot and cold fluids being mixed by the consumer at the point of use in order to compensate for cooler storage tank output temperatures. Sixth, the size of the tank required for storage results in the loss of space that would otherwise be available for other uses. It also limits the possibilities for fluid heater installation to those situations where sufficient space is available. This, in turn, may eliminate the option of installing a fluid heater. Alternatively, it may require its placement at an inappropriate location relative to the point of use, resulting in longer piping, decreased efficiency and a longer period of time to deliver heated fluid to the point(s) of use. Seventh, electric heating element life can be shortened due to extreme differences in heating element temperatures or with higher temperatures of the electric heating element. Often, the heating element(s) located in the storage tank cannot be serviced or replaced without great inconvenience, typically requiring the draining and wasting of fluid in the tank.

The aforesaid difficulties have led to numerous attempts to develop electrically powered instantaneous and/or on demand type fluid heaters. The features of these types of fluid heaters differ widely. Thus, there are numerous variations in the method of power distribution and the nature and design of the heating element(s) utilized, the temperature control means/system utilized (if any), and the manner in which fluid flowing through the device is directed and manipulated. One primary distinction between such fluid heaters relates to the last variable mentioned—the manner in which fluid flowing through the device is directed and manipulated. In this regard, instantaneous fluid heaters may be divided between: (a) those in which fluid to be utilized flows through/past one or more heating vessels/elements before it leaves the apparatus; and (b) those that also rely to some degree on forced recirculation of some portion of the fluid heated thereby through/past these same vessels/elements before it leaves the apparatus. Instantaneous fluid heaters within the first category described, those in which fluid to be utilized flows through/past one or more heating vessels/elements before it leaves the apparatus, range from relatively small and uncomplicated devices of the type utilized for coffee makers or similar uses to much more complicated and larger devices intended for general household, commercial or industrial uses. Typical examples of the smaller type of device may be found in U.S. Patent No. 4,371,777 for a "Continuous Flow Electric Water Heater" and in U.S. Patent No. 4,558,205 for an "Electric Continuous Flow Water Heater Having Dual Temperature Safety Limiting Devices." Typical examples of larger devices within this category may be found in U.S. Patent Nos. 3,230,346 ("Electric Continuous Flow Heater Having a Plurality of Heating Channels"); 3,952,182 ("Instantaneous Electric Fluid Heater"); 4,604,515

("Tankless Electric Water Heater with Staged Heating Element Energization"); 4,808,793 ("Tankless Electric Water Heater with Instantaneous Hot Water Output"); 4,970,373 ("Electronic Temperature Control System for Tankless Water Heater"); and 5,020,127 ("Tankless Electric Water Heater"). Far fewer examples of instantaneous fluid heaters within the second category described, those that rely to some degree on the forced recirculation of the fluid heated in the device to achieve their aims, are to be found in prior art. The first example of such a device known to the inventors is seen in U.S. Patent No. 3,349,755 issued to A. L. Miller in 1967 for a "Recirculating Flow Water Heater" based on steam heating. In the Miller device, which is typical of devices in this category, cold water enters a first plenum which is in communication with the interior of a first plurality of heated tubes. These tubes are, likewise, in communication with the interior of a second plenum. Water is drawn from the first plenum into the second plenum via a pump connected intermediate to second plenum and a third plenum. This pump forces the water received from the second plenum into a third plenum and from there through a second plurality of heated tubes to a fourth plenum. The fourth plenum has a first outlet whereby heated water can be drawn off for use and a second outlet leading back into the first plenum. The rate of flow induced by the pump is substantially greater than the rate of flow induced by the use of the consumer. Thus, a substantial amount of the water entering the fourth plenum after being heated is returned to the first plenum where it mixes with incoming cold water and serves to preheat such water before it is circulated through the heating tubes.

A second example of the recirculating category of instantaneous water heaters is seen in U.S. Patent No.4,046,189 issued to John A. Clark in 1977 for a "Water Heater." The Clark device, like the Miller device described above, relies on steam heating. Unlike Miller, it incorporates a small heat exchange/storage vessel through which water being heated is recirculated. It is, therefore, more representative of a hybrid category of fluid heaters which attempt to combine the features and advantages of instantaneous water heaters with a more limited storage tank than would usually be found in a storage type water heater.

Heretofore, however, instantaneous fluid heaters in both categories set forth above have been subject to numerous problems which have limited their acceptance and use in most applications. Most have lacked the ability to provide extremely accurate temperature regulation across a wide range of flow demands and a concurrent inability to react quickly to changes in flow demands. Instantaneous heaters have generally lacked the ability to safely and/or effectively handle full power in low flow demand situations. The performance of such systems cannot, in most situations, equal or exceed that of conventional storage tank systems in terms of temperature set point maintenance. They may not, therefore, be considered a viable substitute in such situations. In addition, they generally provide an inadequate quantity of heated fluid at the desired set point temperature for the user.

Generally, instantaneous heaters lack flexibility in that most are generally responsive to flow demands only within a narrow band. Thus, those that function well for high flow demands often function poorly in low flow demand situations and vice versa. Some rely on staged energization of heating elements, such that heating elements are activated/energized in increasing numbers as flow demand increases. This often results in significant deviation from the temperature set point when the flow rate varies from the flow rate range at which a certain number of heating element is activated to the flow rate range at which an increased number is activated. These heaters are often characterized by poor temperature set point recovery as demands for flow change during use. They do not usually provide adequate temperature set point regulation when flow demands require less than full rated power. Alternatively, they do not usually provide means for user adjustment of the set point. Prior instantaneous fluid heaters often require specialized heating elements or excessively advanced (and expensive) technology and components (i.e., microprocessors, multiple temperature sensors, microwave heating technology, etc.) for their function. In addition, electric heating element life can be shortened due to extreme differences in heating element temperatures or with higher temperature of the electric heating element. Given that such systems are generally not designed for long term serviceability, the system often must be replaced when malfunctioning. These systems are often limited in terms of their field of use, and are not compatible with usage in a wide variety of industrial, commercial, medical and residential applications, often requiring manufacturers to produce a larger number of specialty products to perform an equal number of applications as compared to storage devices or other instantaneous devices. Finally, these systems are seldom designed in a manner which provides for optimum sediment removal or are not inherently self cleaning.

Summary of the Invention The subject invention pertains to an instantaneous type fluid heater with excellent performance characteristics. It is an object of the subject invention to overcome the previously described limitations and problems associated with instantaneous and storage type fluid heaters. The subject invention provides a fluid heating process and device that is simple and rugged in construction, durable, easily maintained and inherently self cleaning. The subject heater functions efficiently in a great variety of applications within a wide range of flow rates. The subject instantaneous fluid heating device and process with its related subsystems (for fluid manipulation, electrical control, electrical power distribution and temperature control) as taught herein is capable of accurately regulating a preselected fluid temperature set point regardless of suddenly induced changes in flow demands for a virtually unlimited range of varying flow rates, electrical power requirements and applications, and represents a tremendous improvement in performance, reliability, safety, and simplicity as compared to any published data available for other systems known by the inventors.

In a preferred embodiment of the subject invention, forced fluid recirculation past/through one or more heating element(s)/vessel(s) featuring immersible electrical heating element(s) is utilized. The heating element(s)/vessel(s) can be arranged in series with all of said heating element(s)/vessel(s) receiving electricity and being switched on/off simultaneously. Preferably, one or more solid state relays can be used, which respond to a control signal from a temperature control system having a temperature sensor. This temperature sensor can be responsive to the minutest changes in temperature below/above the set point temperature. In a preferred embodiment the subject invention is characterized by a combination of:

(a) forced fluid recirculation past/through heating elements/vessels featuring immersible electric heating elements in one or more heating vessels arranged in series with all of said heating elements/vessels being equal in heating capacity and each having its electricity switched on/off simultaneously; (b) a master electrical control means which features start-up, general control and safety features (as further summarized in section "B," below); and (c) one or more solid state relays which serve as electrical power distribution means for said heating elements and are, preferably, cooled by incoming fluid and can, therefore, simultaneously serve to pre-heat such fluid before it enters the aforesaid heating vessels (as further summarized in section "B," below); and (d) an instantaneously reactive on/off type of temperature control and regulation means (i.e., 7 one having no "dead band" around the temperature set point) which is responsible for providing the on/off control signals to the aforesaid solid state relay(s) and which features an extremely sensitive immersion sensor located within or proximate the intake for the device's recirculation pump and fluid outlet (as further summarized in section "C," below). It is a specific object of the instant invention to overcome the previously described limitations and problems associated with safety and effectively providing electrical power for instantaneous fluid heaters through the provision of master electrical control and electrical power distribution systems suitable for use with same. It will be found that electrical systems constructed in accordance with the teachings of this invention are simple and rugged in construction, durable, easily maintained, and function efficiently in a great variety of applications within a wide range of flow rates and electrical power requirements and can be adapted for use in either static or recirculation types of instantaneous fluid heaters. The electrical systems for instantaneous fluid heating devices taught herein are capable of controlling overall system functions and safely supplying electrical power so as to allow the accurate regulation/control of fluid temperature set point and fast set point recovery when user induced changes in output flow occur. It retains this capability (despite suddenly induced and drastic changes in flow demand) for a wide range of overall electrical power requirements. (This potential requires the ability to rapidly switch high amperage loads between on/off states in response to the minutest perceived changes in temperature). Further, they have proven capable of maintaining this desirable characteristic across a wide range of varying flow rates and should, theoretically, be capable of maintaining this desirable characteristic across an infinite range of flow rates and overall electrical power requirements (as determined/required by a particular application). Moreover, the systems and processes utilized have been found to be simple, safe and reliable, and can be employed in self contained devices or integral systems that provide precise control and regulation of the output fluid temperature in low powered and high powered applications, including residential home water heating applications (in lieu of conventional hot water tanks), and scientific, medical, industrial and commercial applications.

In their most basic embodiments, the electrical systems utilized with the instant invention rely on the utilization of at least one electrical relay (preferably a solid state relay) to relay electricity to the heating element(s) employed in the system, which solid state relay is (a) disposed in such manner as to be actively cooled by incoming fluid, and (b) may be indirectly deactivated by one or more high temperature limiting safety switches, which switches are normally closed, but open at high temperatures (discontinuing necessary control voltage(s)) so as to terminate the supply of electricity to such element(s). In its preferred embodiments, the master electrical control (and safety) system depends on a supply of electricity which may be terminated by thermal safety switch(es) and is activated by an application specific means such as a flow sensing, temperature sensing, and/or manually actuated switch(s), thereby supplying control ("on") voltages to (a) the electrical power distribution system; (b) the temperature control system (which is summarized in more detail in section "C," below); and (c) a pump used for the purpose of recirculating fluid through/past the heating vessels/elements of the device.

In the preferred embodiments of the electrical power distribution system, at least one electrical relay (preferably a solid state relay) is utilized to relay electrical power to the heating elements employed in the system, which solid state relay(s): (a) receive control ("on") voltage(s), depending on the number of relays and their configuration, from the previously described master electrical control or from the temperature control system described below (and is/are, therefore, in both cases, susceptible to being indirectly deactivated by the operation of previously mentioned thermal safety switch(es)); (b) may employ either a single redundant safety system or a double redundant safety system (both being indirectly responsive to the aforesaid thermally actuated high temperature limiting safety switches) for a typical single phase or three phase alternating current voltage supply ("ACv") with (i) single redundant safety requiring at least one solid state relay capable (directly or indirectly) of interrupting the ACv supply to the heating element(s), and (ii) double redundant safety requiring at least one additional solid state relay capable (directly or indirectly) of interrupting the ACv supply and the heating element(s); and (c) said solid state relay(s) are mounted on a heat exchange vessel (or vessels) so as to provide maximum cooling by incoming fluid, which heat exchange vessel (or vessels) can incorporate false activation suppression characteristics (as described, infra) if desirable for the particular application. Upon review it will be found that many of the problems associated with instantaneous type fluid heaters, as detailed in the "Background" Section above, are due to, or exacerbated by, the lack of temperature detection/control systems or the slow response speed of the temperature detection/control systems utilized by same. Thus, it is a specific object of the temperature control system utilized in the instant invention to overcome the previously described limitations and problems through the provision of a temperature control system that, like the fluid heating system it supports, is instantaneous in operation. This has been accomplished through the provision of a temperature control system that is simple in construction, durable, and functions efficiently in a great variety of applications and within a wide (and possibly infinite) range of flow rates. The temperature control system and process for instantaneous fluid heating devices taught herein greatly facilitates the accurate regulation of fluid temperature set point despite suddenly induced changes in flow demands. Further, it is capable of maintaining this desirable characteristic across a wide (and possibly infinite) range of carrying flow rates (as determined by the application). In its most basic preferred embodiments it relies on and is characterized by: (a) a purely reactive on/off type of temperature control and regulation means which is instantly responsive to (b) an extremely sensitive (i.e., "fast") immersion sensor located within the recirculation path proximate the outlet port for the instantaneous fluid heater. Thus, it is designed in such a manner as to have no inoperative dead band around the temperature set point and, therefore, can respond instantly to perceived changes in the temperature set point. (It should be noted that other forms of temperature control such as proportional, PID, fuzzy logic, and staged as commonly known within the art could be used to achieve satisfactory temperature regulation). In its preferred embodiments, as illustrated herein, the aforesaid system may advantageously be utilized in conjunction with the novel electrical power distribution system also developed by the inventors and described herein. The system and process utilized have been found to be simple, safe and reliable, and can be employed in a self contained device for low powered applications or in an integral system for higher powered applications. It allows for user adjustment of the fluid output temperature by means of a temperature set point adjustment control. In operation, when the temperature sensor senses the smallest rise or fall above or below the selected set point temperature, the temperature control system instantly signals one or more electrical relays

(preferably solid state electrical relays) to terminate or apply electric power to all heating elements simultaneously, irrespective of the amount (which may be infinitesimal) the temperature has risen or fallen, in order to maintain the temperature set point. In this manner, the output temperature can be closely maintained relative to the set point from extremely low flow rates to flow rates faster than the heater's ability to maintain the set point temperature with the heating elements remaining on continuously.

Greater efficiency can be achieved when the total power applied to the heating elements is essentially equal to the precise power that is required to maintain a desired output set point temperature. It is desirable to maintain the desired output set point temperature regardless of changes in Process Dynamics. Accordingly, the resulting heated fluid temperature can be essentially equal to the desired set point temperature under a variety of conditions.

In a specific embodiment, the subject invention provides a single electronic temperature control device, particularly well suited for Instantaneous Devices, which can be applied to numerous applications regardless of electrical scale or applications for use. Temperature control 10 devices constructed in accordance with this invention provide excellent performance for a variety of alternating current applications, for example 120 VAC, 208 VAC, 240 VAC, 480 VAC, single phase, three phase. The device of the subject invention does not require a multitude of different electronic temperature control devices for use with different Instantaneous Devices. Another feature of the subject invention is an electrical power distribution device applicable to Instantaneous Devices that is controllable from one temperature control device, regardless of the electrical power requirement. In a preferred embodiment, the voltage and amperage requirement of the heating elements may vary for different fluid heating devices while the temperature control device can be essentially universal. The subject invention can provide precise temperature regulation during Idle Use periods immediately following active use, when it is desirable to prevent internal fluid temperatures from significantly rising above the selected set point temperature.

Temperature control devices constructed in accordance with the subject invention can reduce the need for an electronic calibration mode in addition to a normal operation mode. The subject temperature control devices can be field adjusted or factory adjusted to compensate for the differences in the specific heat of fluids other than water, or, to compensate for differently powered applications. In a specific embodiment, the specific heat or power requirement may be sensed as input data variables, negating the need for any adjustment for any practicable fluid heating application in order to control the process up to the rated power. Embodiments of the subject invention that rely on Common Temperature Control Devices described herein as part of an overall embodiment for a fluid heating device may or may not require pre-tuning.

Brief Description of the Drawings

Figure 1 illustrates, in conceptual fashion, the overall process and interrelationship between the physical, electromechanical, electrical, and electronic components of the apparatus and process utilized in the instant invention. In particular, it illustrates the interrelationship of forced recirculation, simultaneous on/off switching of heating elements through the temperature control means, and double redundant power distribution in one preferred embodiment.

Figure 2 provides a view from above of a preferred embodiment of the instant invention.

Figure 3 provides a first side view of a preferred embodiment of the instant invention taken along line A— A of Figure 2.

Figure 4 provides a second side view (at right angles to that provided in Figure 3) of a preferred embodiment of the instant invention taken along line B— B of Figure 2. 11

Figure 5 provides a third side vιew(at πght angles to that provided in Figure 4 and from the opposite side from that provided m Figure 3) of a preferred embodiment of the instant invention taken along line C--C of Figure 2.

Figure 6 provides, in schematic form, a detailed view of all electπcal systems of the instant invention, including the circuit diagram of the essential circuits employed m the preferred embodiment of the master electrical control system, the temperature control system, and (by way of illustrative example and not of limitation) the preferred embodiment of the double redundant electπcal power distribution system described in more detail with respect to Figure 8.

Figure 7 illustrates, m schematic form, a first embodiment of the temperature control and electrical power distribution and safety systems taught by this invention, which first embodiment incorporates a single redundant high temperature responsive safety means. (See, also, Figure 6, component 112).

Figure 8 illustrates, in schematic form, a first preferred embodiment of the temperature control and electπcal power distπbution and safety systems taught by this invention, which first preferred embodiment incorporates a first type of double redundant high temperature responsive safety means. (See, also, Figure 6, component 301b).

Figure 9 illustrates, in schematic form, a second preferred embodiment of the temperature control and electπcal power distribution and safety systems taught by this invention, which second preferred embodiment incorporates a second type of double redundant high temperature responsive safety means.

Figure 10 provides a side view of a first configuration for the disposition of solid state relays so as to allow their cooling while in operation by incoming fluid on a unit incorporating false activation suppression means.

Figure 11 provides a cross-sectional view taken along D--D of Figure 10 of a first configuration for the disposition of solid state relays so as to allow their cooling while in operation by incoming fluid on a unit incorporating false activation suppression means.

Figure 12 provides a first side view of a second configuration for the disposition of solid state relays so as to allow their cooling while in operation by incoming fluid on a unit incorporating false activation suppression means. Figure 13 provides a second side view (at πght angles to that provided in Figure 12) of a second configuration for the disposition of solid state relays so as to allow their cooling while m operation by incoming fluid on a unit incorporating false activation suppression means.

Figure 14 provides a first side view of a third configuration for the disposition of solid state relays so as to allow their cooling while m operation by incoming fluid. 12

Figure 15 provides a second side view (at πght angles to that provided m Figure 14) of a third configuration for the disposition of solid state relays so as to allow their cooling while in operation by incoming fluid.

Figure 16 provides an approximate actual size side view of a microminiature thermistor probe assembly employed in the preferred embodiment of the temperature control system charactenzing the instant invention.

Figure 17 provides a magnified cross-sectional view of the tip of the microminiature thermistor probe assembly employed in the preferred embodiment of the temperature control system characterizing the instant invention. Figure 18 provides a transparent oblique view of a fluid heater containing components of the vaπous embodiments with the exception of the electronic temperature control devices.

Figure 19 provides, in schematic form, an overall view of the electrical system for a fluid heater including an analog control method for proportioning electπcal power to the heating source. Figure 20 provides, in conceptual form, an overall view of a digital method for proportioning electrical power to the heating source, as utilized for indirect temperature regulation or flow augmentation temperature regulation devices.

Detailed Disclosure of the Invention As illustrated in Figures 1 through 5, the Instantaneous Fluid Heating Device taught herein is compact m configuration. (This is, in fact, one of its major advantages over conventional tanks). In its most basic embodiments it may be considered to be comprised of four basic subsystems: (a) a basic fluid heating and recirculation structure; (b) a master electπcal control system; (c) an electπcal power distribution system; and (d) a temperature control system The basic physical structure (i.e., the fluid heating/recirculation structure) of the device is descπbed in Section I, below. The master electπcal control systems for the device are descπbed in Section II, below. Its electπcal power distribution system is descπbed in Section III, below. Finally, its temperature control systems are descπbed in Section IV, below. Notwithstanding its simplicity, the synergistic combination of the preferred embodiments of these systems m the preferred embodiment of this invention has been able to achieve results, in expeπmental prototypes, which far exceed those of any electrically powered storage or instantaneous fluid heating device known to the inventors. I. Basic Fluid hea ing and Recirculation Structures

The fluid heating/recirculation structure charactenzing the instant device and its operation may best be understood by reference to Figures 1 through 5, where a specific 13 embodiment of the subject invention is illustrated. As will be noted, the device taught herein is provided with an inlet port 1, which is in communication with an outside source of fluid to be heated (not shown). Upon entering the device via inlet port 1, in a specific embodiment, such fluid can flow into a heat exchange vessel 2, upon which can be mounted a first solid state relay (hereinafter designated as the "control relay 3") and a second solid state relay (hereinafter designated as the "safety relay 4"). The fluid can receive heat from these relays in order to enhance the efficiency of the subject fluid heater. After preferably being preheated via the heat released from these relays the fluid can enter the main heater core, which can be comprised of one or more heating vessels, preferably of equal volume and electrical power (i.e., of equal heating capacity), with the exact number of heating vessels, heating elements and the fluid volume of each heating vessel being application specific.

In the specific embodiment illustrated in Figures 2 through 5, four such heating vessels are utilized. Thus, after exiting the heat exchange vessel 2, the preheated fluid can enter the first heating vessel 5 where heat is applied by the first heating element 6. (See, Figure 3). As fluid leaves the first heating vessel 5 it progresses through first connector 7 to the second heating vessel 8 where additional heat is applied via the second heating element 9. In the embodiment illustrated, fluid then flows via second connector 10 to the third heating vessel 11 where the fluid collects additional heat from the third heating element 12. (See, Figure 4). The fluid flows through the third connector 13 to the fourth heating vessel 14 where it receives heat from the fourth heating element 15. (See, Figure 5).

After the fluid has flowed through all of said heating vessels in sequence, and before exiting past the flow switch 102 (See Figure 2) via the outlet port 16 (see, Figure 4), the majority of the heated fluid is recirculated past an enclosed immersion type microminiature thermistor probe assembly 20 (see, Figures 1, 2, 3, 5, 16 and 17) through a suitable conduit 17 back into the first heating vessel 5. This recirculation can be accomplished by, for example, a sealless, magnetic drive pump 18 attached to conduit 17 between fourth heating vessel 14 and first heating vessel 5. While the apparatus is in operation, recirculation can be continuous, with the exact speed of recirculation also being application specific. Heated fluid being drawn off can exit the apparatus via the outlet port 16. A temperature and pressure relief valve (T&P valve 19) can be provided as an automatic emergency release valve for overheated fluids from the device.

A valve that will release at 150 PSI and/or 210°F may advantageously be utilized for this purpose.

Referring to the embodiment illustrated in Figures 2-5, the following numbers are given as only exemplary of a system for use in a situation where a maximum demand rate of 14 approximately 3 gallons per minute is encountered: (1) total internal fluid capacity of the heating structure of about ³Λ gallon; (2) power consumption of the electric heating elements of about 16000 watts; and (3) recirculation rate of recirculation pump of about 7 gallons per minute. In reviewing the specific physical embodiment described in this section the following should be borne in mind: The specific physical embodiment of the primary heat exchange vessel(s) (i.e., heating vessels 5, 8, 11 and 14, and associated heating elements) responsible for heating the fluid itself, while still conforming to the fluid heating process developed by the inventors, is a function of application specific requirements based on, for example, the desired warm-up time for heating the fluid, the desired maximum outflow of heated fluid, the desired maximum heated temperature of the fluid, the maximum allowable transfer rate of heat to the fluid itself, the maximum allowable rate of forced recirculation of the fluid itself, the response time of the temperature sensor utilized, and the maximum allowable temperature deviation above and below the desired set point temperature. Thus, as these functions directly impact the variable design characteristics of the primary heat exchange vessel(s), numerous design constants, such as total fluid capacity, total elecfrical kilowatt power of the heating elements, the speed or presence of forced fluid recirculation, the total number of heating elements used, the mass of fluid heating structure, and the number of heating vessels employed, may be varied to meet specific design objectives.

In a preferred embodiment, greater efficiency and performance is achieved by applying essentially the precise electrical power that is required to maintain the fluid temperature, by manipulating the power to match the required electrical power. Combining the subject teachings applicable to Instantaneous Devices, either exclusively or in conjunction with other Common Temperature Control Devices can result in the provision of an essentially unlimited stream of precisely heated fluid, without regard to changes in Process Dynamics. The heating process can be activated by an application specific means, for example a flow sensing, pressure sensing, temperature sensing, or manually actuated device. Activation can consist of applying electricity to a control device or devices responsible for, for example, electrical power distribution, temperature regulation, and safety.

In a preferred embodiment, at least one electrical relay conducts essentially equal amounts of electricity to one or more heating elements essentially simultaneously. These can be, for example, immersion heating elements. The fluid can flow through a heater core composed of one or more heating chambers that contain one or more immersion heating elements, with the exact number of heating chambers and heating elements being application specific. With regard to said electrical relay(s), these can have on/off or proportional output 15 stages, as commonly referred to in the art. For example, various types of relays are commonly refeπed to as SSR, SCR, Triac, Diac, Thyrister, or phase angled. An alternative relay embodiment can be utilized for staged fluid heating devices (i.e., those devices that apply electrical power to each heating source individually, rather than equally and simultaneously as described herein.)

In a preferred embodiment, a temperature control device maintains the output temperature essentially constant regardless of changes in the volumetric demand for heated fluid. Such a temperature control device can be analog or digital, as is commonly known in the art. In a preferred embodiment, temperature regulation is accomplished by sending an appropriate control signal to the input stage of the Relay(s) in order to control all electrical heating elements essentially equally and essentially simultaneously. In one example of temperature control of a fluid passing through an Instantaneous Device, a temperature confrol device can provide essentially the precise minimum power required to maintain a precise set point temperature. This temperature control device can accommodate changes in the temperature of a fluid entering the process or changes in the discharged fluid flow rate.

In a specific embodiment, the subject invention can respond to changes in fluid flow demands by varying the power to the heating source in a non-linear, proportional manner. In this embodiment the amount of power applied to the heating source can be varied in response to, for example, a selected temperature range or band. This temperature range is commonly referred to as a proportional band, occurring between a first reference temperature and a lower second reference temperature. When the actual temperature is within the proportional band, an equal portion of the total power is applied to the heating source per an equally corresponding change in temperature in such a manner that 0% of power is applied when the actual temperature is essentially equal to the first reference temperature, and 100% of power is applied when the temperature is essentially equal to the second reference temperature. A common variation to this approach is to create a portion of the total power relative to the actual temperature across the proportional band, and is commonly referred to as proportional with integral derivative (PID) control. Conventional PID controllers do not directly consider the flow rate as an input for determining the integral or derivative function, but rather, merely shift the proportional or integral derivative function(s) whenever the temperature deviates from the intended set point in response to a perceived change in output temperature over time. In the subject invention, the normally linear portion of power applied to the heating source relative to the flow demand can be fixed along a non-linear curve modeled over a specific flow range, power requirement, and temperature range. 16

One approach to such a temperature control device is to (i) provide the fluid temperature of a fluid, for example fluid exiting the process, as input data to the temperature control device; (ii) calculate or otherwise determine essentially the precise electrical power required to maintain the desired set point temperature from the input data in a manner that considers the rate of fluid discharge from the fluid heating device; (iii) apply the calculated electrical power to the heating elements; (iv) continuously repeat steps (i) through (iii) for as long as practicable for an application; and (iv) optionally, recirculate a majority of the fluid, for example as described herein, before the fluid exits the fluid heating process. In this way, the resulting output temperature will be essentially constant at all times regardless of changes in the volumetric demand for heated fluid.

Another approach to such a temperature control device is to (i) provide the fluid temperature of a fluid, for example, entering (or exiting) the process, and the demand flow rate as input data to the temperature control device; (ii) calculate or otherwise determine essentially the precise electrical power required to maintain the desired set point temperature from the input data; (iii) apply the calculated electrical power to the heating elements; (iv) continuously repeat steps (i) through (iii) for as long as practicable for an application; and (v) optionally, recirculate a majority of the fluid, for example as described herein, before the fluid exits the fluid heating process. In this way, the resulting output temperature is essentially constant at all times, regardless of changes in the process dynamics for an application as represented by the input data. The input data represented in this example are as follows: (i) the temperature of a fluid, for example entering (or exiting) the process, and (ii) the rate of fluid discharge. The input data can be application specific, and may include one or more variables as input data to the process.

In a preferred embodiment of a temperature control device, it is not necessary to sample the heated discharge fluid temperature, as is common in the art, in order to precisely control the process. This can be referred to as Indirect Temperature Regulation. However, it is still possible to achieve a high degree of precision by sampling the heated discharge fluid temperature as is previously accomplished with Common Temperature Control Devices in conjunction with sampling the fluid discharge flow rate (or other process dynamics), in order to maintain essentially precise output fluid temperatures. Thus, in an alternative embodiment of this invention, the control signal can be from a PID, Fuzzy logic, On/off, proportional, proportioning, pulse, or other Common Temperature Control Device (or signal), as commonly known in the art. In addition, faster warmup times are achieved when full power is applied until the temperature approaches the set point temperature, as is common in the art. 17

In an alternative embodiment, staged energization of the heating elements may be employed in a manner that yields similar results. Such an approach will require confroling individual circuits to the different heating elements. Embodiments that employ staged energization of the heating elements, or other Common Temperature Control Devices described herein, can employ sensing (or other derivation) of discharge fluid flow and use the derived/sensed data in conjunction with the fluid temperature in order to regulate the discharge fluid temperature. This technique is hereinafter referred to as Flow Augmentation. With regard to Flow Augmentation, this concept can be applied to other Process Dynamics as described herein, and this technique is referred to as Process Augmentation. In a specific embodiment comprising multiple heating chambers, as the heated fluid exits the last heating chamber of the heater core, a portion of the fluid can be recirculated back into the first heating chamber at the beginning of the normal fluid flow path and through the remaining heating chambers of the heater core by means of a pump, before the fluid being heated finally exits the process. If there is only one heating chamber a portion of the exiting fluid can be recirculated back to the fluid entry location of the heating chamber in much the same way.

If this form of recirculation is introduced, then mixing occurs between the fluid entering the heater core and the fluid having already passed through the heater core. This recirculation further reduces temperature variations that could otherwise exist upon extreme changes in output flow demands, or during periods of constant flow demands when cannot sufficiently regulate the fluid temperature at all times.

Furthermore, it is possible to vary the rate of recirculation as changes in output demand flow, or changes in other Process Dynamics, occur. When varying the recirculation rate, consideration for the ability of the heater core material to gain or lose heat should be given, i.e., the specific heat of the material. Varying the recirculation rate in this way can cause a brief, inversely proportional, change in the output fluid temperature with respect to the change in the recirculation rate. Therefore, it is possible to counteract the normally characteristic drop in output temperature, for example, when the demand for fluid suddenly or drastically increases, by briefly decreasing the recirculation rate from the said normally static rate of recirculation. The recirculation rate can then be gradually returned back to the normally static rate of recirculation.

Likewise, it is possible to counteract the normally characteristic rise in output temperature, for example, when the demand for fluid suddenly or drastically decreases, by briefly increasing the recirculation rate from the normally static rate of recirculation. Again the rate can be gradually returned back to the normally static rate of recirculation. In essence, the 18 rate of heat fransfer to the fluid is manipulated. Changing the recirculation rate can either temporarily reduce the rate of heat imparted to the fluid as recirculation increases, or temporarily increases the rate of heat imparted to the fluid as recirculation decreases, resulting in a brief controllable change in temperature relative to the desired set point until, for example, the heater core and fluid stabilize at essentially the same temperature.

In an additional embodiment, a device can employ a normally constant rate of recirculation which can be manipulated by varying the normally constant rate of recirculation and maintaining different constant recirculation rates with respect to certain changes in Process Dynamics. For example, in a device which utilizes a Common Temperature Confrol Device such as PID, On/Off, proportional, or staged, the introduction of recirculation as described herein can significantly improves temperature stability with regard to changes in Process Dynamics. The presence, absence, or rate of fluid recirculation can be manipulated via, for example, on/off or variable speed pumps, fluid control valve(s), or a combination of said pump(s) and valve(s).

II. Master Electrical Control System

A. Overview of System

The master electrical confrol system 112 for the device can best be understood by reference to Figure 1 (which provides a conceptual overview of the entire invention) in conjunction with Figure 6 (which includes additional diagrams of the temperature control system 110 for the device and one embodiment of its electrical power distribution and safety system

301b). Turning to Figure 6, it will be noted that the master electrical control system 112 (which can include components 101, 102, 103, 104, 105, 106, and 107, and is also referred to herein as the "MEC") for the device can include a series of normally closed bimetallic thermal safety switches 101. These bimetallic thermal safety switches 101 conduct low amperage AC voltage to the normally open flow switch 102 and the normally open secondary circuit 103b of start relay 103. Electricity is conducted by flow switch 102 when closed. Flow switch 102 is, in turn, solely responsible for providing electricity to primary circuit 103a of start relay 103. Upon closing of the primary circuit 103a of start relay 103, the secondary circuit 103b of start relay 103 closes and provides AC voltage to a miniature ACV/ACV step down transformer 104 and recirculation pump 18. The reduced voltage output from transformer 104 provides input voltage to DC bridge rectifier 105 which provides low DC voltage output. Capacitor 106, which is connected in parallel across outputs of bridge rectifier 105, reduces AC voltage ripple to within acceptable limits. Voltage regulator 107 provides regulated DC voltage Voutl to the inputs of the components comprising the temperature confrol and electrical power distribution systems 19 of the instant invention at points labeled Vinl in Figure 6. The start relay 103 could also, advantageously, have a time delayed secondary to aid in false activation suppression. The reasons for this feature (i.e., false activation suppression) and other solutions to the problem of false activation are described in more detail in Section III, below.

B. Indirect Deactivation Feature

As previously noted, the master electrical control system 112 provides confrol voltages to the temperature control system 110 and the pump 18. It may optimally be designed to provide such confrol voltages when engaged and when triggered by flow switch 102 when there is a fluid flow through the device, when manually actuated, and/or through some other application specific means. The master electrical control 112 is, however, ultimately dependent for electrical power upon one or more bimetallic thermal safety switches 101, as previously discussed. Each bimetallic thermal safety switch is in thermal communication with the fluid in the device via physical contact with heat conducting surfaces of the device. Thus, if the temperature of the system rises to the rated limit of any of the thermal safety switches 101 they or it will serve to interrupt the flow of electrical power to the master electrical control 112 which provides confrol voltages to the pump 18 and the temperature control system 110. When the flow of electricity to the temperature control system 110 is terminated by the opening of any of the normally closed bimetallic safety switches 101, the temperature control system 110 cannot, in turn, provide primary or control voltages to the control relay 3, thereby opening circuit 111 and terminating the flow of electrical power to the heating element(s) 6, 9, 12, and 15 (jointly denoted 401 in Figure 1). (It will also be noted that the circuit encompassing these heating elements should advantageously be provided with fuses F6, F9, F12, and F15 as illustrated in Figures 6, 7, 8, and

9). The provision of indirect deactivation means is rendered more desirable due to the possible employment of high powered elecfrical heating elements, which can be utilized for certain fluid heating applications, and the need to respond quickly and reliably to the potential for rapid overheating which could result, regardless of the heating power required for such applications (in the unlikely event of system failure). An additional advantage of indirect deactivation is that it allows the use of bimetallic thermal safety switches rated for low amperage loads. Direct deactivation by bimetallic thermal safety switches wired in series with the electrical heating element(s) would require several thermal safety switches rated for the full amperage of the electrical heating element(s) being deactivated. Conversely, indirect deactivation allows the use of much smaller, faster, less expensive bimetallic thermal safety 20 switches. Further, with regard to direct deactivation, bimetallic thermal safety switches rated for the high amperage electπcal loads envisioned for many projected applications of this device do not exist. In a specific embodiment, the bimetallic safety switches 101 utilized are V_ inch, bimetallic, matte finish discs which are encased in a sealed housing and affixed to heating vessels 5, 8, 11, and 14, at the points of highest potential external temperature, utilizing a suitable heat sink compound. The synergistic combination of these design features as a means for providing reliable and rapid response to possible overheating for theoretically unlimited application specific fluid heating power requirements is, to the best of the inventors' knowledge, unknown m the pπor art.

III. Elecfrical Power Distribution and Safety System

The electπcal power distribution and safety system charactenzing this invention can best be understood by reference to Figure 1 in conjunction with Figures 6 through 15. As noted in Section I, above, fluid enteπng the device via inlet 1 preferably initially traverses a heat exchange vessel 2 on which is mounted at least one solid state electrical relay (control relay 3).

(See, generally, Figures 1 through 5). The confrol relay 3 serves pπmaπly to relay electrical power from an alternating voltage source external to the device to the electπcal heating elements of the device m response to the master elecfrical confrol means 112 described m Section II, above. This external source is denoted as Acv in Figure 1 and Figures 6 through 9 and is illustrated as a single phase in these drawing figures for ease of understanding; however, this invention could easily be adapted for three phase operation by those skilled in the art.

The addition of heat exchange vessel 2 intermediate inlet 1 and first heating vessel 5 and the positioning of control relay 3 thereon (as illustrated in Figures 1 through 5 and Figures 10 through 15), serve two important purposes. First, the confrol relay 3 is actively cooled by the flow of incoming unheated fluid. Second, while serving as a heat sink for the control relay 3, the fluid traversing the heat exchange vessel 2 can be preheated pπor to entry into the first heating vessel 5. This serves to improve the overall efficiency and performance of the device by reducing the amount of heat necessary to be transferred to the fluid by heating elements 6, 9, 12, and 15, productively utilizing incoming energy that would otherwise be lost as waste heat from the control relay 3, and helping to heat the fluid pπor to its entry into the first heating vessel 5 while simultaneously providing cooling to relays 3 and 4.

Even with the added safety produced by the presence of active cooling of the electrical relays utilized, it is advantageous to safeguard the system and the user from the possibility that, either by the unlikely failure of some system component or for some other reason, electrical 21 power will continue to flow to the heating elements even when the temperature of the fluid being heated has reached levels in excess of those deemed safe for the system. Thus, the embodiment illustrated can incorporate one of three application specific safety features, as can best be appreciated by reference to Figures 7, 8 and 9 which illustrate, in schematic fashion, the overall configuration for electrical power distribution in three embodiments of the instant invention.

The first and simplest embodiment of the electrical power distribution and safety system, as illustrated in Figure 7, is a basic single redundant safety system wherein thermal safety switches 101 (which will, as discussed in Section II, above, disengage the flow of electricity to the temperature confrol system 110 if the system temperature becomes too high) provide a back-up to the safeguards provided by the system's temperature confrol system 110.

The basic elecfrical power circuit 111 for the device runs from an appropriate external source of alternating elecfrical voltage (ACv) to the heating elements 6, 9, 12, and 15. However, the circuit 111 can only be closed and electricity supplied to heating elements 6, 9, 12, and 15 when the primary of confrol relay 3 (designated as primary 3a) receives an appropriate control voltage (designated as Vout2) from temperature control system 110, closing the secondary of control relay 3 (designated as secondary 3b).

Temperature control system 110 provides a confrol voltage Vout2 only when the temperature of the fluid falls below a certain "set point" temperature established by the user. Thus, the temperature control system 110 serves as a first level of protection, as it will only engage the control relay 3 when the temperature of the fluid is below a certain set point temperature. Likewise, it serves to interrupt the flow of electricity to the control relay 3 when fluid temperature rises above the aforesaid set point temperature. The addition of one or more bimetallic thermal safety switches 101 in the circuit intermediate the source of elecfrical power ACv and the temperature control system 110, as discussed in Section II, above, provide a first level of redundancy. Such as system is, therefore, referred to in its system embodiment as a single redundant system.

Notwithstanding the added safety provided to the invention by the single redundant safety system described above, the inventors deem it advantageous, in the preferred embodiments of this invention, to utilize one of two basic types of double redundant safety systems, as illustrated schematically in Figures 8 and 9. In a double redundant safety system, an additional relay (denoted as safety relay 4 in Figure 8 and second control relay 4 in Figure 9) is provided in the system. As illustrated in Figure 8, this additional relay (safety relay 4) may receive its primary voltage input directly via the master electrical control 112 (Voutl). In the alternative, as illustrated in Figure 9, the additional relay (second control relay 4) may receive 22 its primary voltage input via the temperature control system 110 output (Vout2). In both cases, however, an additional (or double redundant) safeguard is provided against system failure in the form of a failure of the control relay 3 to disengage upon termination of control voltage (Vout2) from the temperature control system 110 to its primary (3a). Three possible variations for the design and configuration of the heat exchange vessel

2 utilized in conjunction with the electrical power distribution and safety system are illustrated in Figures 10 through 15. The first configuration, as illustrated in Figures 10 and 11, is horizontally disposed. The second configuration, as illustrated in Figures 12 and 13, is vertically disposed and features four solid state relays to accommodate the increased electrical power demands envisioned for its application. (See, Figures 14 and 15). As will be noted upon review of Figures 10 through 13, the design may allow for a fluid level less than the total volume of the heat exchange vessel 2. The remaining space in each heat exchange vessel 2 is filled with trapped air which acts as a buffer against and helps to suppress false activation of the flow switch 102 of the instant invention due to the pressure fluctuations that normally occur in plumbing systems when non-heated fluid is demanded from the same plumbing system. It should also be noted that heat sink compound may be advantageously used to connect the relays previously described to the heat exchange vessel 2 so as to allow for more efficient heat exchange. (This also allows for maximum heat transfer from the relay(s) to the fluid).

Referring now to Figure 18, a specific embodiment of a fluid heater in accordance with the subject invention is shown. Electrical activation of the heating system can be accomplished when, for example, a fluid flow is sensed by a flow sensing device 102. An embodiment which employs either Indirect Temperature Regulation or Flow Augmentation as described herein, can advantageously rely upon a flow rate measuring device as shown in Figure 20. Referring back to Figure 18, outside fluid enters through an inlet port 1, flowing into the power distribution unit 2 past an optional baffle 26 that separates the power distribution unit 2 from the heater core 400.

Baffle 26 can be utilized in an embodiment which relies upon recirculation in order to provide improved cooling of relay 3. In an embodiment which employs Indirect Temperature Regulation as described herein or Flow Augmentation as described herein, baffle 26 may be eliminated. Fluid can pass from power distribution unit 2 into heater core 400 through passage(s) 27. At least one Relay 3 can be affixed to the power distribution unit 2, for example, in a manner that allows for cooling of Relay 3. Relay 3 can interrupt power to one or more heating elements 6,9,12,15 when, by fault, at least one strategically placed high temperature limit switch(es) senses fluid temperatures above a predetermined hi-limit safety temperature. 23

Relay 3 can provide power to the heating elements via a signal received from a temperature controller, which regulates power through Relay 3 to the heating elements 6,9,12,15. The heat generated at the base of relay 3 can be absorbed by the inflowing fluid, thus preheating the fluid and recapturing otherwise wasted energy before the fluid flows from the power distribution unit 2 into heater core 400. The preheated fluid flows into fluid heating core 400 past heating elements 6,9,12,15 where the fluid collects further heat. In an embodiment which utilizes recirculation, the fluid can be optionally recirculated within heater core 400 by, for example, drive pump 18, to reduce the temperature difference between the fluid exiting heater core 400 and the fluid entering heater core 400. Such recirculation can improve temperature set point stability and recovery with regard to static and changing flow rates. The heated fluid can exit the heater past the flow switch 102 and through the outlet port 16.

Referring now to Figure 19, a schematic view of an electrical system, including analog control for proportioning electrical power to a heating source, is shown. ACv is a suitable voltage supply source from, for example, an external power source. Such voltage is commonly described in the art as 120 volt, 208 volt, 240 volt, or 480 volt, single phase, three phase, etc., and can be application specific. ACv is supplied when the system is activated. ACv can continuously supply voltage to the primary circuit of at least one Relay and power to the electric heating elements through the Relay's secondary circuits while the system is activated. This voltage can be automatically discontinued by deactivation of one or more strategically placed thermally actuated bimetallic safety switches 101, at which point all control voltages can cease, thus shutting down the system in the event of a malfunction. While the system is activated under normal operation, appropriate control voltages, for example Voutl, can also be supplied to a temperature control device as described herein.

In an embodiment which utilizes recirculation, an optional relay 108, which can incorporate a time delayed shut-off to drive pump 18, can be advantageously used to delay the shut-off of pump 18 when the demand for fluid ceases. Delaying the shut-off of the pump in this manner greatly reduces the potential of a significant temperature rise that can occur after the demand for heated fluid ceases.

IV. Temperature Confrol System

The temperature control system utilized in the instant invention may best be understood by reference to Figures 6 through 9, 16 and 17 in conjunction with Figure 1 and the previously discussed figures related to the electrical power distribution and safety system (Figures 6 through 9). Figure 6 provides a circuit diagram of the essential circuits employed in the 24 prefeπed embodiment of the temperature confrol system 110 characterizing the instant invention. (See, components numbered 20, 212, 213, 214, 220, 221, 222, 223, 224, 230, and 232, of Figure 6). As will be noted, the circuits utilized may be divided, and may be classified generally, into three sections. The first such section, which serves as the temperature sensing and voltage linearization section, is comprised of: (1) a regulated low voltage input source Vinl supplied by the master electrical control 112 (Voutl in figure 6); (2) the microminiature thermistor 21 described below; (3) a calibration resistor 212 for the linearization bridge; and (4) a first adjunct bridge resistor 213 and second adjunct bridge resistor 214 forming the rest of the linearization bridge. (An RTD may be substituted for the thermistor, thereby eliminating the need for linearization circuitry). The second section, which serves as the differential amplification section, is comprised of a first operational amplifier 220. If the resistance of fourth op-amp resistor 224 is equal to the resistance of second op-amp resistor 221, then the voltage output of first operational amplifier 220 equals the resistance of fourth op-amp resistor 224 divided by the resistance of third op-amp resistor 223 times the result of the input voltage labeled "-" of first operational amplifier 220 subfracted from the input voltage labeled "+" of first operational amplifier 220 (or R224/R223 (⁺V - ^"V)). The third section, which forms the comparator section for the circuit, is comprised of a second operational amplifier 230 whose voltage output Vout2 is the on/off trigger for the primary circuits 3a of (the preferably solid state) control relay 3 which relays or interrupts the electrical voltage supplied to the heating elements 6, 9, 12, and 15, and a potentiometer 232 utilized for setting the output set point temperature/voltage equivalent. (Control relay 3 relays electrical power in response to the presence of absence of Vout2 at the primary confrol input 3a of control relay 3). As will be noted, the input from the differential amplification section serves as the reference voltage for the second operational amplifier 230. The unique feature of the above-described circuitry is that it is instantly reactive and there is, therefore, no "dead band" around the set point. It is, in effect, an on/off system in which switching is instantaneous in response to perceived changes in temperature. This allows the heating system utilizing the temperature control system described herein to be switched on and off in slow cycles or extremely rapid bursts as the need therefor naturally occurs and such is necessary to maintain set point temperature and to correct deviations in set point stability that would otherwise result. Thus, in contrast to the slower reacting systems in current usage, which lag in reacting to a signaled decrease in the temperature of the fluid being heated, and (just as importantly) lag in terminating the heating process after receiving a signal that the heat of the fluid exceeds the set point, this system is capable of responding instantaneously. This allows 25 far more sensitive and concise temperature confrol than has heretofore been achieved without expensive or excessive technology such as microprocessors or computerized control.

However, having solved the problem of creating a system that is instantaneous in its response to a signaled change in fluid temperature solves only part of the concerns addressed by this invention. The extreme efficiency with which the above described system will function is ultimately dependent on the sensitivity of the temperature probe or sensor utilized by the device (i.e., the speed with which a recognizable signal is provided to the temperature confrol system by the temperature probe utilized). To address this issue, the subject invention can utilize an ultra-fast microminiature thermistor 21 (which is connected to the aforementioned linearization bridge section of the temperature control system 110 via leads 23 contained in the temperature probe 20). See for example, Figures 16 and 17. In preferred embodiments of this invention, a microminiature thermistor 21 with a time constant of 1 second (still air to still air), one of the most sensitive available, placed in a stainless steel immersion housing 22 with a time constant of .7 seconds (still air to still water), has provided extremely satisfactory results. Microminiature thermistor probe assemblies of this type may be acquired (upon providing specifications therefor) from several electronics manufacturers.

Referring again to Figure 19, a first conditioned voltage potential, derived from a suitable temperature sensing device 21, can serve as a signal essentially representing the temperature of a fluid exiting the process. A thermistor as shown, a thermocouple, RTD, or other common sensor known in the art, can be employed to generate the temperature signal.

Such a sensor can rely on the commonly known supportive circuitry known in the art and normally associated with such sensors. A specific embodiment can employ measuring resistance, amperage, infrared, electronic pulses, or signal from a suitable device to represent the fluid temperature. The temperature indication signal can be submitted as a first and second parallel input to a first operational amplifier 220. The balance of components 212-224 are as described herein. The output signal from the first operational amplifier 220 can be submitted as a first parallel input to a second operational amplifier 240 through resistor 243. Potentiometer 232 provides a second parallel input to operational amplifier 240. Resistors 241-244 form a differential amplifier. The output of operational amplifier 240 is the difference of the first parallel voltage supplied from first operational amplifier 220 subfracted from the second parallel voltage supplied from potentiometer 232.

Operational amplifier 250 can be configured as a transconductance amplifier 600, where the resulting proportional output current of vout2 from operational amplifier 250 essentially 26 drives the input 3a of Relay 3. Resistor 251 can be sized in a manner that creates a non-linear proportional output from secondary 3b of Relay 3. The non-linear output provided by resister 251 can compensate for temperature deviations that would otherwise occur as the discharge rate of flow from the instantaneous fluid heating device increases or decreases. The output 3b of Relay 3 can essentially drive electric heating elements 6,9,12,15 essentially equally and simultaneously, in a proportional manner. This can provide the desired set point temperature, essentially at all times, with respect to changes in discharge fluid flow. An alternative embodiment can use a digital device that includes a microprocessor in lieu of the circuit contained in box 110A. Another specific embodiment can use pulsewidth modulator integrated circuits, etc. in lieu of, or in addition to, operational amplifiers 220,240 and 250 to derive signal

Vout2. Another embodiment can utilize recirculation as described herein.

Referring now to Figure 20, an overall view of a digital method for proportioning electrical power to the heating source is shown. In a specific embodiment, a first conditioned voltage potential, for example derived from a suitable temperature sensing device 20, can serve as a signal representing the temperature of a fluid entering the process. This embodiment can employ a thermistor, thermocouple, RTD, or other common sensor known in the art, to acquire the temperature signal. Such an embodiment can rely on commonly known supportive circuitry associated with such sensors. A specific embodiment can employ measuring resistance, amperage, electronic pulses, or other signal to represent the fluid temperature. A second conditioned voltage potential derived from a suitable flow sensing device 25 can serve as a signal representing the rate of flow discharged from the fluid heating device. An alternative embodiment may employ, for example, measuring resistance, electronic pulses, amperage or other signal to represent the rate of flow discharged. The flow sensing device 25 can be placed at any strategic position where the rate of fluid discharge is obtainable. In lieu of flow sensing device 25, an analog or digital circuit can alternatively calculate or otherwise derive the fluid flow rate from other process variables in lieu of reliance upon a flow sensing device 25.

The first conditioned voltage potential and the second conditioned voltage potential can be converted to equivalent digital signals with A/D (analog/digital) converter 501 and A/D converter 502, respectively. If input sensors 20 or 25 are electronic pulse devices, then A/D conversion is not necessary for the respective pulse signal. The converted digital signals from A/D converter 501 and A/D converter 502 can be inputted to a microprocessor 500, where a series of programed instructions can be used to produce an output signal via microprocessor 500. 27

This output signal can represent a power factor required to achieve a specified temperature for the fluid exiting the fluid heating device.

The logical instructions processed by microprocessor 500 can employ indirect regulation algorithms as described herein, as necessary m deπving the power factor. In a preferred embodiment, the power factor will represent the actual power requirement itself without further manipulation. The Digital output signal from microprocessor 500 can be converted to an analog signal, by D/A converter 503, appropπate for the hardware supporting microprocessor 500 One example is shown in Figure 19, box 600. The resulting output signal from D/A converter 503 can serve as a control signal fed into at least one relay input 3a. At least one relay output 3b can drive at least one electric heating element 401, essentially equally and simultaneously, in a proportional manner. Digital signals from A/D converter 501 and A/D converter 502 can be repeatedly sampled and processed by microprocessor 500, m order to essentially proportion the power applied to heating element(s) 401, thus providing the desired set point temperature m realtime. In an alternative embodiment, a more elaborate approach may be employed in order to provide electrical power to heating element 401 through, for example, sampling of input potentials from temperature sensor 20 and flow sensor 25. In another embodiment, an analog device constructed of integrated circuits can be used m lieu of the microprocessor 500 to perform the function of deriving the heating element power requirement from the inlet fluid temperature and flow rate. Such an embodiment can employ, for example, operational amplifiers, voltage/resistance multiplier/divider linear integrated circuits, or pulsewidth modulator integrated circuits, to deπve the power requirement for regulating fluid temperature. In an embodiment for an instantaneous device that includes a Common Temperature Control Device in lieu of the embodiment shown in Figure 20, electπcity can be provided to all electπcal heating elements essentially equally and essentially simultaneously in order to precisely regulate the fluid temperature. In such an embodiment, or other staged embodiment where electricity is not provided to all electπcal heating elements essentially equally and essentially simultaneously, recirculation can be utilized, wherein each may deπve the output fluid temperature from the introduction of Flow Augmentation. Again, referring to Figure 20, m a specific embodiment, a first conditioned voltage potential derived from a suitable temperature sensing device 20 can serve as a signal representing the temperature of a fluid exiting the process. This embodiment can have temperature sensor 20 located proximate the outlet port 16 of the fluid heater 400, instead of being proximate the inlet port 1 as shown This embodiment can employ a thermistor, 28 thermocouple, RTD, infrared or other common sensor known in the art, to acquire the temperature signal. For example, sensor 20 can be placed in, or past, the fluid heater core 400. Such an embodiment can rely on commonly known supportive circuitry associated with such sensors. Additional embodiments can employ measuring resistance, amperage, electronic pulses or other signals to represent the fluid temperature.

A second conditioned voltage potential derived from a suitable flow sensing device 25 can serve as a signal representing the rate of flow discharged from the fluid heating device. An alternative embodiment can employ measuring resistance, electronic pulses, amperage or other signal to represent the rate of flow discharged and the flow sensing device 25 can be placed, for example, at any strategic position where the rate of fluid discharge is obtainable. An additional embodiment can calculate, or otherwise derive, the fluid flow from other process variables in lieu of reliance upon a flow sensing device 25. A first conditioned voltage potential and a second conditioned voltage potential can be converted to their respective equivalent digital signals by A/D converter 501 and A/D converter 502. Converted digital signals from A/D converter 501 and A/D converter 502 can be inputted to a microprocessor 500 where a series of programed instructions can be processed to determine an output signal from microprocessor 500 that represents an essential power factor required to achieve a specified temperature for the fluid exiting the fluid heating device from digital input signals acquired from A/D converter 501 and A/D converter 502. The logical instructions processed by microprocessor 500 can employ Flow Augmentation algorithms, as necessary in deriving the power factor. In the prefeπed embodiment, the power factor will represent the actual power requirement itself without further manipulation.

The Digital output signal from microprocessor 500 can be converted to an analog signal by D/A converter 503. The resulting output signal from D/A converter 503 can serve as a control signal fed into relay input 3. For example, the circuit shown in Figure 19, box 600, can be used for this purpose. At least one relay output 3b can drive at least one electric heating element 401, essentially equally and simultaneously, in a proportional manner. Digital signals from A/D converter 501 and A/D converter 502 can be repeatedly sampled and processed by microprocessor 500, in order to adjust the power applied to heating element(s) 401, in order to provide the desired set point temperature, in essentially realtime.

An additional embodiment can use an analog device constructed of integrated circuits and/or discrete electronic components, in lieu of the microprocessor 500, to perform the function of determining the heating element power requirement from the fluid temperature and flow rate. Such an alternative embodiment can employ, for example, operational amplifiers, 29 voltage/resistance multiplier/divider linear integrated circuits, or pulse width modulator integrated circuits, to determine the power requirement for regulating fluid temperature. In an embodiment of the subject invention that includes a Common Temperature Control Device in lieu of other variations described herein, electricity can be provided to all electrical heating elements essentially equally and essentially simultaneously, in order to precisely regulate the fluid temperature. The introduction of recirculation as described herein and/or the introduction of indirect temperature regulation as described herein can also enhance performance in embodiments where electricity is not provided to all electrical heating elements essentially equally and essentially simultaneously. As will be obvious upon review of the foregoing, numerous variations are possible without exceeding the ambit and scope of the inventions described herein. It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and the scope of the appended claims.

Claims

30 Claims

1. An electrical power distribution device for use in a fluid heating device, said fluid heating device utilizes at least one elecfrical heating element receiving electricity from a source of electrical power to heat fluid flowing through the fluid heating device so that said fluid is proximate a set-point temperature upon exiting from said fluid heating device, comprising: a heat exchange vessel formed of heat conducting materials, said heat exchange vessel (i) serves to relay a fluid in a fluid heating device, and (ii) has at least one flat exterior surface wherein said at least one flat exterior surface is incorporated into a wall of said heat exchange vessel; and at least one electrical relay disposed upon said at least one flat exterior surface of said heat exchange vessel in such manner as to be in thermal communication with the fluid flowing through said heat exchange vessel such that said at least one electrical relay is cooled by said fluid.

2. An electrical power distribution device for use in a fluid heating device, as described in claim 1, wherein said at least one engageable electrical relay is a solid state electrical device.

3. An electrical power distribution device for use in a fluid heating device, as described in claim 1 , wherein said heat exchange vessel includes false activation suppression means based upon the inclusion of an air space within said heat exchange vessel.

4. An electrical power distribution device for use in a fluid heating device as described in claim 1 , wherein the interior of said heat exchange vessel is provided with multiple interior heat exchange surfaces formed from heat conducting materials, said multiple interior heat exchange surfaces in thermal communication with the heat conducting materials forming the heat exchange vessel in such manner that heat exchange takes place between the said heat exchange vessel and the said multiple interior heat exchange surfaces.

5. A temperature confrol device for use in a fluid heating device, said fluid heating device utilizes at least one elecfrical heating element receiving electricity from a source of electrical power to heat fluid flowing through the fluid heating device so that said fluid is proximate a set-point temperature upon exiting from said fluid heating device, comprising: 31 at least one elecfrical relay which serves to relay electrical power essentially simultaneously to all electrical heating elements in response to the temperature of a fluid.

6. A temperature control device, as described in claim 5, wherein said at least one electrical relay provides essentially a minimum amount of elecfrical power required to maintain said fluid exiting from said fluid heating device at said set-point temperature.

7. A temperature control device, as described in claim 5, further comprising: a means for sensing a temperature of a fluid exiting said fluid heating device; and a means for determining a proportional amount of electrical power, based on said temperature, to apply to the electric heating elements to maintain said fluid exiting said fluid heating device proximate said set-point temperature.

8. A temperature control device, as described in claim 5, wherein the amount of electrical power relayed to the electrical heating elements by said at least one elecfrical relay is based on a predetermined power curve, wherein said predetermined power curve compensates for process dynamics specific to an application.

9. A temperature control device, as described in claim 5, wherein said temperature control device is selected from the group consisting of a PID, a fuzzy logic device, and an artificial intelligence device.

10. A temperature control device, as described in claim 5, wherein said temperature sensor is an immersible micro-miniature thermistor assembly.

11. A temperature control device, as described in claim 5, further comprising a temperature sensor responsive to a low voltage input source, a voltage linearization section responsive to said temperature sensor, a differential amplification section responsive to said voltage linearization section, and a comparator section responsive to said differential amplification section.

12. A temperature control device, as described in claim 11, wherein said temperature sensor is an immersible micro-miniature thermistor assembly.

32 13. The temperature confrol device, according to claim 11, wherein said comparator section compnses a potentiometer utilized for setting an output set point temperature/voltage equivalent.

14. A temperature control device, as described m claim 13, wherein said temperature sensor is an immersible micro-mmiature thermistor assembly.

15. A temperature confrol device for use in a fluid heating device, wherein said temperature control device utilizes a rate of flow of fluid exiting the fluid heating device to determine an amount of power required to maintain said fluid exiting said fluid heating device at a set-point temperature.

16. A temperature control device, as desc╧Çbed in claim 15, wherein said temperature control device utilizes a temperature of fluid exiting the fluid heating device to determine an amount of power required to maintain said fluid exiting said fluid heating device at said set-pomt temperature.

17. A temperature control device, as described m claim 15, wherein said temperature control device utilizes a temperature of fluid ente╧Çng the fluid heating device to determine an amount of power required to maintain said fluid exiting said fluid heating device at said set-pomt temperature.

18. A temperature control device, as desc╧Çbed m claim 15, wherein said temperature control device is selected from the group consisting of a PID, a fuzzy logic device, and an artificial intelligence device.

19. An engageable master elecfrical control device for providing safety m a fluid heating device utilizing at least one elecfrical heating element to heat fluid flowing through the fluid heating device comp╧Çsing: at least one elect╧Çcal supply relay having a p╧Çmary and a secondary, wherein a confrol voltage is applied to the p╧Çmary of said at least one elect╧Çcal supply relay, the secondary of said at least one elect╧Çcal supply relay being part of an elect╧Çcal circuit supplying elect╧Çcal power to at least one elect╧Çcal heating element; and 33 an engageable safety means wherein said engageable safety means is electrically isolated from said electrical circuit that supplies electrical power to said at least one elecfrical heating element and wherein said engageable safety means terminates flow of electrical power to said at least one electrical heating element upon said safety means detecting a temperature within said fluid heating device above a safety-point temperature.

20. An engageable master elecfrical control device, as described in claim 19, further comprising an engageable elecfrical start relay which must be engaged in order for said control voltage to be supplied to said primary of said at least one electrical supply relay.

21. An engageable master electrical control device for use in a fluid heating device, as described in claim 20, further comprising a false activation suppression means which includes the use of a time delayed electrical relay as said engageable electric start relay.

22. An engageable master electrical control device, as described in claim 20, wherein said engageable safety means is responsive to the temperature of a fluid being heated, wherein said engageable safety means must be engaged in order to relay elecfrical power to engage said elecfrical start relay, and wherein said engageable safety means only engages said engageable electrical start relay while the temperature of the fluid being heated is below the safety point temperature.

23. An engageable master electric control device, as described in claim 19, wherein said engageable safety means comprises at least one bimetallic thermal safety switch in thermal communication with the fluid being heated.

24. An engageable master electric control device, as described in claim 19, further comprising an overall engagement means, which means must be engaged in order for said engageable master electrical control means to be engaged.

25. An engageable master elecfrical control device, as described in claim 24, wherein said overall engagement means comprises a flow switch which only engages said master electrical control means in response to a fluid flow.

34 26. An engageable master electrical control device for use in an instantaneous fluid heating device, as described in claim 19, wherein said engageable master elecfrical confrol means includes false activation suppression means.

27. A fluid heating device that receives electricity from a source of elecfrical power in order to heat fluid flowing through said fluid heating device so that said fluid is proximate a set- point temperature upon exiting from said fluid heating device, comprising: a fluid heating structure, said structure (i) having an inlet through which the fluid being heated enters the fluid heating structure, (ii) having an outlet through which the fluid being heated exits the fluid heating structure, and (iii) comprising of at least one vessel with each of said at least one vessel having at least one electrical heating element such that the fluid entering the inlet of the fluid heating structure flows through each of said at least one vessel past said at least one electrical heating element contained in each of said at least one vessel before exiting through the outlet of said fluid heating structure, wherein elecfrical power is supplied essentially simultaneously to all electrical heating elements in order to regulate a fluid temperature.

28. The fluid heating device, according to claim 27, further comprising an engageable temperature control means responsive to the temperature of the fluid, and only engages at least one engageable electrical relay which supplies electrical power to said elecfrical heating elements while said engageable temperature controls means is engaged.

29. The fluid heating device, according to claim 27, wherein said set-point temperature can be adjusted by a user.

30. A fluid heating device as set forth in claim 27, further comprising an engageable fluid recirculation means, wherein said engageable fluid recirculation means recirculates a portion of the fluid being heated back into the fluid heating structure before said fluid being heated exits the fluid heating structure.

31. The fluid heating device, according to claim 30, wherein said fluid is recirculated back into the fluid heating structure proximate the inlet.

35 32. The fluid heating device, according to claim 31, wherein said fluid is drawn for recirculation from proximate the outlet.

33. A fluid heating device as set forth in claim 27, further comprising: an electrical power distribution means having a heat exchange vessel, said heat exchange vessel being formed of heat conducting materials, wherein said heat exchange vessel (l) serves to relay a fluid being heated to the mlet of said fluid heating structure and (n) has at least one flat exte╧Çor surface wherein said at least one flat exterior surface is incorporated into a wall of said heat exchange vessel; and at least one engageable electrical relay disposed upon said at least one flat exterior surface of said heat exchange vessel in such manner as to be m thermal communication with the fluid flowing through said heat exchange vessel such that said at least one engageable electrical relay is cooled by said fluid.

34. A fluid heating device as set forth m claim 27, further comprising: an elect╧Çcal power dist╧Çbution means having a heat exchange vessel, said heat exchange vessel being formed of heat conducting materials, wherein said heat exchange vessel (I) serves to relay a fluid being heated to the mlet of said fluid heating structure and (n) has at least one flat exte╧Çor surface wherein said at least one flat exterior surface is incorporated into a wall of said heat exchange vessel; and at least one engageable elecfrical relay disposed upon said at least one flat extenor surface of said heat exchange vessel in such manner as to be in thermal communication with the fluid flowing through said heat exchange vessel such that said at least one engageable electrical relay is cooled by said fluid.

35. A fluid heating device, as set forth in claim 33, further comp╧Çsing engageable master elecfrical control means having: at least one elect╧Çcal supply relay having a p╧Çmary and a secondary, wherein a control voltage is applied to the p╧Çmary of said at least one elect╧Çcal supply relay, the secondary of said at least one elect╧Çcal supply relay being part of an elecfrical circuit supplying elect╧Çcal power to said at least one electrical heating element contained m each of said at least one vessel; and an engageable safety means, wherein said engageable safety means is electrically isolated from said electrical circuit that supplies electrical power to said at least one electrical heating element, wherein said engageable safety means terminates flow of elect╧Çcal power to 36 said at least one electrical heating element upon said safety means detecting a temperature within said fluid heating device above a safety-pomt temperature

36. A fluid heating device as described in claim 27, further comp╧Çsing a flow switch which only engages said engageable master elect╧Çcal control means when fluid is being emitted from said outlet

37. A fluid heating device as desc╧Çbed in claim 35, further comprising a flow switch which only engages said engageable master electrical control means when fluid is being emitted from said outlet.

38. A fluid heating device, as set forth in claim 27, wherein each of said at least one vessel is approximately equal in heating capacity.

39. A fluid heating device, as set forth in claim 35, wherein each of said at least one vessel is approximately equal in heating capacity.

40. A fluid heating device that receives elect╧Çcity from a source of electrical power m order to heat fluid flowing through said fluid heating device so that said fluid is proximate a set- point temperature upon exiting from said fluid heating device, comp╧Çsing: (a) a fluid heating structure, said structure (l) having an mlet through which the fluid being heated enters the fluid heating structure, (n) having an outlet through which the fluid being heated exits the fluid heating structure, and (m) comp╧Çsing at least one vessel, with each of said at least one vessel having at least one electrical heating element such that the fluid flows through each of said at least one vessel past said at least one electrical heating element contained in each of said at least one vessel before exiting through the outlet of said fluid heating structure; (b) an engageable fluid recirculation means which when engaged recirculates a portion of the fluid being heated back into the fluid heating structure before said fluid being heated exits the fluid heating structure.

41. The fluid heating device, according to claim 40, wherein said fluid is recirculated back into the fluid heating structure proximate the mlet.

37 42. The fluid heating device, according to claim 40, wherein said fluid is drawn for recirculation from proximate the outlet.

43 The fluid heating device, according to claim 40, wherein said set-pomt temperature can be adjusted by a user.

44. A fluid heating device as described in claim 40, further comprising: an elecfrical power dist╧Çbution means wherein said electrical power distribution means includes a heat exchange vessel formed of heat conducting materials, wherein said heat exchange vessel (l) serves to relay a fluid being heated to the inlet of the fluid heating structure, and (n) has at least one flat exterior surface which said at least one flat exterior surface is incorporated into a wall of said heat exchange vessel; and at least one engageable elecfrical relay disposed upon said at least one flat exterior surface of said heat exchange vessel in such manner as to be in thermal communication with the fluid flowing through said heat exchange vessel such that said at least one engageable electrical relay is cooled by said fluid.

45. A fluid heating device as desc╧Çbed in claim 40, wherein all of said heating elements are engaged essentially simultaneously.

46. A fluid heating device, as desc╧Çbed in claim 40, further comp╧Çsing an engageable master elecfrical confrol means having: at least one elect╧Çcal supply relay having a p╧Çmary and a secondary, wherein a control voltage is applied to the p╧Çmary of said at least one elect╧Çcal supply relay, the secondary of said at least one elect╧Çcal supply relay being part of an elect╧Çcal circuit supplying elect╧Çcal power to said at least one electrical heating element; and an engageable safety means, wherein said engageable safety means is electrically isolated from said elecfrical circuit that supplies elecfrical power to said at least one elecfrical heating element, wherein said engageable safety means terminates flow of electrical power to said at least one elecfrical heating element upon said safety means detecting a temperature within said fluid heating device above a safety-point temperature.

47. A fluid heating device, as desc╧Çbed in claim 45, further comprising an engageable master electrical confrol means having: 38 at least one elect╧Çcal supply relay having a p╧Çmary and a secondary, wherein a control voltage is applied to the p╧Çmary of said at least one elect╧Çcal supply relay, the secondary of said at least one elect╧Çcal supply relay being part of an elecfrical circuit supplying electrical power to said at least one electrical heating element; and an engageable safety means, wherein said engageable safety means is electrically isolated from said electrical circuit that supplies electrical power to said at least one electrical heating element, wherein said engageable safety means terminates flow of elect╧Çcal power to said at least one elecfrical heating element upon said safety means detecting a temperature withm said fluid heating device above a safety-pomt temperature.

48. An instantaneous fluid heating device as described in claim 46, further including a flow switch which only engages said engageable master electrical control means when fluid is being emitted from said outlet.

49. An instantaneous fluid heating device, as set forth in claim 40, wherein each of said at least one vessel is approximately equal in heating capacity.

50. An instantaneous fluid heating device, as set forth m claim 45, wherein each of said at least one vessel is approximately equal m heating capacity.

51. A method for heating a fluid, said method comp╧Çsing the steps of (1) passing a fluid through a fluid heating device, wherein said fluid heating device compnses a means for heating fluid; and (2) recirculating said fluid withm the fluid heating device.

52. The method according to claim 51, wherein said means for heating fluid utilizes a heat source selected from the group consisting of: natural gas, propane, fossil fuel, steam, and electncity.

53. The method, according to claim 52, wherein said fluid is recirculated at a rate of recirculation greater than a rate of fluid exiting from the fluid heating device.

54. The method, according to claim 52, wherein said fluid is recirculated at a rate of recirculation greater than a maximum rate of fluid exiting from the fluid heating device. 39

55. The method, according to claim 52, wherein recirculation of said fluid is triggered by fluid exiting from the fluid heating device.

56. The method, according to claim 55, wherein termination of recirculation is delayed, after the cessation of fluid exiting from the fluid heating device, to reduce temperature rises fluid near the heating element.

57. The method, according to claim 52, wherein said method maintains fluid exiting the fluid heating device proximate a fluid set-pomt temperature.

58. The method, according to claim 57, wherein said fluid set-pomt temperature is selectable.

59. The method, according to claim 57, wherein said fluid heating device maintains fluid exiting the fluid heating device proximate a fluid set-pomt temperature by heating fluid to be discharged contemporaneously with demand for such heated fluid.

60. The method, according to claim 52, wherein said means for heating a fluid compnses at least two elecfric heating elements, wherein said electricity is supplied to said at least two elecfric heating elements m a staged manner.

61. The method, according to claim 51, wherein said fluid heating device further compnses at least one vessel having at least one elecfric heating element such that fluid entenng the fluid heating device flows through each of said at least one vessel, past said at least one elecfric heating element, before exiting the fluid heating device.

62. The method, according to claim 61, wherein elecfric power is supplied essentially simultaneously to all elecfric heating elements when heating the fluid.

63. The method, according to claim 61, wherein electric power is supplied to said elecfric heating elements m a staged manner.

40 64. The method, according to claim 57, further comprising the step of applying essentially the precise elecfric power needed to maintain the fluid exiting the fluid heating device at said fluid set-pomt temperature.

65. The method, according to claim 51 , wherein activation of said at least one electric heating element is controlled by a device selected from the group consisting of: a flow sensor, a pressure senor, a temperature sensor, and a manual device.

66. The method, according to claim 62, wherein the elecfric power supplied to said elecfric heating elements is supplied by one or more electrical relays, wherein said relays have an output stage selected from the group consisting of: an on/off output stage and a proportional output stage.

67. The method, according to claim 63, wherein the electric power supplied to said elecfric heating elements is supplied by one or more elect╧Çcal relays, wherein said relays have an output stage selected from the group consisting of: an on/off output stage and a proportional output stage.

68. The method, according to claim 67, wherein the elecfrical relays are selected from the group consisting of: SSR, SCR, Triac, Diac, Thy╧Çster, and phase angled.

69. The method, according to claim 67, wherein said fluid heating device utilizes a temperature control device selected from the group consisting of: a PID, a fuzzy logic device, and an artificial intelligence device.

70. The method, according to claim 57, further comprising the step of: varying a rate of recirculation of the fluid withm the fluid heating device, wherein varying the rate of recirculation assists in maintaining the fluid exiting the fluid heating device at the fluid set-point temperature.

71. The method, according to claim 57, further comprising the steps of: monitonng a rate of fluid exiting the fluid heating device; and 41 varying a rate of recirculation of the fluid within the fluid heating device in response to changes in the rate of fluid exiting the fluid heating device in such a manner as to assist in maintaining the fluid exiting the fluid heating device proximate the fluid set-point temperature.

72. A fluid heating device which heats fluid flowing through the fluid heating device such that fluid exiting the fluid heating device is proximate a set-point temperature, comprising: a means for receiving fluid to be heated; a means for heating fluid; a means for recirculating fluid within the fluid heating device; and a means for discharging fluid which has been heated, wherein said fluid heating device discharges fluid proximate a set-point temperature, upon demand for fluid, by heating fluid to be discharged contemporaneously with such demand.

73. The fluid heating device, according to claim 72, wherein said means for heating fluid utilizes a heat source selected from the group consisting of: natural gas, propane, fossil fuel, steam, and elecfricity.

74. The fluid heating device, according to claim 72, wherein said means for recirculating fluid within the fluid heating device directs fluid which would otherwise be discharged from the fluid heating device to be combined with fluid received by said means for receiving fluid to be heated.

75. The fluid heating device, according to claim 74, wherein a majority of fluid which would otherwise be discharged from the fluid heating device is directed to be combined with fluid received by said means for receiving fluid to be heated.

76. The fluid heating device, according to claim 74, wherein a rate of recirculation is higher than a maximum rate of discharge.

77. The fluid heating device, according to claim 72, wherein said means for heating fluid comprises at least one elecfric heating element, wherein said fluid heating device comprises a vessel through which fluid flows, and wherein as fluid flows through said vessel the fluid contacts one or more of said at least one elecfric heating element, and is heated when said one or more of said at least one electric heating element is electrified. 42

78. The fluid heating device, according to claim 77, wherein the electric power supplied to said elecfric heating elements is supplied by one or more elecfrical relays, wherein said relays have an output stage selected from the group consisting of: an on/off output stage and a proportional output stage.

79. The fluid heating device, according to claim 78, wherein said fluid heating device utilizes a temperature control device selected from the group consisting of: a PID, a fuzzy logic device, and an artificial intelligence device.

80. The fluid heating device, according to claim 77, wherein each of said at least one elecfric heating element is electrified essentially simultaneously.

81. The fluid heating device, according to claim 80, wherein each of said at least one elecfric heating element is proportionally electrified.

82. A fluid heating device, wherein a rate of flow of fluid discharging from said fluid heating device is utilized to determine an amount of power required to maintain said fluid discharging from said fluid heating device at a set-point temperature.

83. The fluid heating device, as described in claim 82, wherein a temperature of fluid discharging from the fluid heating device is utilized to determine an amount of power required to maintain said fluid discharging from said fluid heating device at said set-point temperature.

84.The fluid heating device, as described in claim 82, wherein a temperature of fluid entering the fluid heating device is utilized to determine an amount of power required to maintain said fluid discharging from said fluid heating device at said set-point temperature.