LIQUID HEATER AND CONTROL SYSTEM TO CONTROL THE LIQUID OUTPUT TEMPERATURE
Field of the Invention The present invention relates to a heater for heating liquids (typically water) to provide a temperature output from which it can be precisely controlled within established limits. The heater of the present invention has been specially designed to heat water, and will be described with particular reference to heat water, but it will be appreciated that the heater could also be used for a variety of other liquids. The heater of the present invention is particularly suitable for domestic water heating or light industrial scale. Background of the Invention For many years, the most common method of heating domestic water was to heat water using electric heating elements or gas burners, and to keep the water heated in an insulated storage pond. However, due to the well-established drawbacks of this method (the requirement for a large isolated pond, and the loss of energy in pre REF: 128286 to heat water and then trying to keep it at temperature, possibly for long periods) several types of appliance offer "instant" water heating are gaining in popularity. The "instant" water heaters are all of one type of flow-through, in which water is heated by gas or by electricity as the water flows through the apparatus. gas have a reasonably high efficiency but a very poor security services sheet: - there have been numerous instances of suffocation or poisoning, and still some cases of explosions when the heaters have operated abnormally.The flow-through water heaters electrically heated They are intrinsically somewhat safer than gas-heated heaters but can compete only with relatively low water flow rates.In addition to the drawbacks described above, flow-through water heaters currently on the market in general are expensive to operate. manufacture and install, with an operational life of only a few years, especially in areas where calcification strong or other deposits must be expected. It is therefore an object of the present invention to provide a water heater which can be manufactured and installed at a relatively low cost, which is electrically energized, but which can contend with acceptably high rates of water flow. A further objective of the present invention is the provision of a water heater which is capable of controlling the temperature of the outlet water within a relatively narrow temperature range: a high degree of control over the exit temperature increases the safety of the device and sub- sistically reduces the operating cost of the device.
Description of the Invention The present invention provides the combination of a liquid heater and a control system for controlling the temperature of the liquid outlet from the heater, wherein the heater is an electrically energized heater at network frequency that includes a coreless transformer having primary and secondary windings of electrically conductive material, the secondary winding being electrically isolated from the primary winding, but disposed relative to the primary winding such that the magnetic flux generated by alternating electric current flowing in the primary winding in use links the winding. secondary winding and induces a voltage there inside; and the control system incorporates a control device to control the power supplied to the heater; characterized in that: a path is provided through the heater, through which the liquid to be heated flows in use; the heater incorporates an electrically conductive molding; the primary winding is arranged to at least partially surround the molding, but is electrically isolated from the molding; the secondary winding is electrically connected to the molding, such that the molding is heated by resistance heating when a voltage is induced in the secondary winding; the control system includes a liquid flow sensor for sensing liquid flow to the heater, the liquid flow sensor being adapted to prevent the supply of electrical power to the heater unless the sensor senses a liquid flow greater than a predetermined minimum flow rate; The control system further includes a probe adapted to measure the temperature of the output liquid and the control device is adapted to regulate the supply of electrical power to the heater in response to the temperature measured by the probe. The control device may include an electronic control panel or a thermostat. Preferably, the control device includes an electromechanical switch in series with a solid-state relay switch adapted for fast on / off interruption; Both of these switches are connected between the power source and the heater such that both switches must be closed before the power can be supplied to the heater. Preferably also, the control system further includes a heater cut-off switch secured to the heater and a winding temperature cut-off switch secured to the primary winding; both the circuit breaker switches are adapted to interrupt the power to the heater if the temperature of the heater or primary winding exceeds a predetermined temperature respectively. Preferably the molding, the primary winding and the secondary winding are all substantially concentric. The primary winding can encircle the secondary winding in the molding or the secondary winding can encircle the primary winding and molding. Preferably, the molding is formed with a passageway through which the liquid to be heated flows in use. Brief Description of the Drawings Fig. 1 is a schematic side view of a heater according to the present invention and the associated control system, with the cover removed; Fig. 2 is a longitudinal section through a first preferred embodiment of the heater of the present invention; Fig. 3 is a longitudinal section through a second preferred embodiment of the heater of the present invention; and Fig. 4 is a flow diagram of the control sequence for the heater.
BEST MODES FOR CARRYING OUT THE INVENTION With reference to Fig. 1, a water heater 2 according to the present invention is generally cylindrical in its shape and is secured by supports 3 at each end to the bottom section of a protective housing (not shown). The half of the tip of the housing may be uncovered to expose the heater 2 and its control system 4 for assembly and maintenance purposes. The internal structure of the water heater 2 is shown in Fig. 2. The heater is circular in cross-section. The central portion of the heater is formed by a molding 5 which may be solid or hollow, that is to say the shaded portion, with crossed lines 5a may be present or may be empty space. The molding 5 should be made of an electrically conductive material, preferably a metal having a relatively high electrical resistance and preferably, but not essentially, made of a ferromagnetic metal (for example ductile steel). The outer cylindrical surface of the molding 5 supports a cylindrical metal jacket 6 (typically copper or aluminum) which is a pressure adjustment on the outer surface of the molding and forms a secondary winding. The pressure adjustment between the molding 5 and the secondary winding 6 ensures a good heat conduction and forms an electrical connection. Since the water to be heated passes over the outer surface of the secondary 6 it is preferred to line the outer surface of the secondary with a stainless-steel jacket 6a, which fits snugly on the secondary winding 6 and prevents contact between the water and the secondary winding. A primary winding 7 is supported by an insulated cylindrical former 8 that encircles but is spaced from the secondary 6. The primary winding 7 is made of multiple turns of insulated copper or aluminum wire and is electrically insulated from the secondary 6. Space 9 between the former 8 and the secondary 6 / 6a are in communication with the inlet 10"and the outlet mouth 11 and with the space 5a if present.The ends of the space 9 are closed by the end caps 12, 13, which they open inside the inlet mouth 10 and the outlet mouth 11. The outer surface of the heater is protected by the insulating sleeve 14.
Fig. 3 shows a second preferred embodiment of the invention, which is designed to give a longer path of flow to the water to be heated. In the preferred embodiment shown in Fig. 3, the heater 20 has an inlet mouth 21 at the same end of the heater as the outlet mouth 22, such that the water to be heated first flows downwards - of a passageway 23 between the outer shell 24 of the heater and a cylindrical metal jacket 25 forming part of a composite secondary winding 25 / 25a, and then flowing through a passageway 26 formed by a pipe 26a which is press-fitted through the center of a central molding 27, to reach the outlet 22. The primary winding 28 is made of multiple turns of copper or aluminum wire wound "on a first insulation jacket 28a, around the outer surface of the molding 27 with a second layer insulator 29 between primary and secondary windings Secondary winding 25 / 25a is a composite: - a metal jacket 25 (typically copper or aluminum) is press fit onto the surface ie outside of a metal tube 25a (typically stainless steel). The secondary winding is electrically connected to the central molding 27. The preferred embodiments described above with reference to Fig. 2 and 3 are both essentially coreless transformers in combination with a molding that provides at least part of a flow path through the core. which flows the liquid to be heated. Coreless transformers have known advantages over core transformers: - lower production costs, improved magnetization characteristics, and greater ease of cooling. However, although coreless transformers are well known, they are usually used only for high frequency applications (typically 50kHz and above), since it is an accepted principle that for frequency transformers in the network it is "possible to obtain a efficient flow only if a core is used, while in high frequency applications it is possible to achieve an efficient flow link between the primary and secondary windings without a core.In view of this accepted knowledge, it was therefore surprising to find that in the present invention, the heater was able to operate at very high efficiency without a core, although it was used at grid frequency In use, the power is applied to the primary winding 7/28; preferably, the heater is energized by the network, i.e. AC, mono or multi-phasic current. The current in the primary winding gives rise to a magnetic flux, which in turn induces a voltage in the secondary winding 6 / 6a / 25 / 25a. Since the secondary winding is electrically connected to the molding 5/27, the current in the secondary winding produced by the induced voltage passes through to the molding, heating the molding by resistance heating. The higher the electrical resistance of the molding material, the greater the resistance heating of the molding. The molding does not need to be made of a ferromagnetic metal, since it does not function as a transformer core: - the only thing is that the molding is made of an electrically conductive material. However, it is advantageous if the jacket is made of a metal fer romagné t i co, because this increases the magnetization of the heater and thus improves its power factor. In addition, the fluctuating magnetic field created when the power is supplied to the primary winding produces eddy current heating in the molding. Eddy current heating would be greater in the preferred embodiment of Fig. 3, because the primary 28 lies close to the molding, but would occur to a lesser degree even in a configuration such as that of Fig. 2, where the secondary lies between the primary and the molding. The molding is also heated by hysteresis heating from hysteresis losses. Both the primary and secondary windings are heated in use, due to heating by metal resistance of the windings caused by the currents flowing through the windings. This heating effect can be reduced by selecting metals that are of high electrical conductivity (eg copper or aluminum) for the primary and secondary windings. However, depending on the design of the heater, it may be possible to use the heating of the windings constructively, to heat the liquid passing through the heater; in this case, the windings can be made of metals of lower electrical conductivity (for example steel), to increase the resistance heating effect since this heat can be used to heat the liquid. Windings should not be allowed to overheat, because this reduces their efficiency and, if the overheating is excessive, it would damage or even destroy the heater. In the preferred embodiment of Fig. 2, the secondary winding 6 / 6a is cooled both by its contact with the molding 5 and by the liquid passing through the space 9. The primary winding 7 is cooled by its location adjacent to the winding. outer surface of the heater, and by the liquid passing through the space 9. In the preferred embodiment of Fig. 3, the secondary 25 / 25a is cooled by the liquid passing through the space 23 and the primary is cooled by its proximity to the molding 27. If a greater cooling of one or the other of the windings the primary and / or secondary is needed, it is possible to design the heater so that the liquid to be heated passes over both sides of that winding, or even to forming the winding as a hollow tube through which the liquid passes. The primary and secondary windings can be formed in any known manner for example as sleeves, tubes, or as wire spools, and can be formed in one or more parts. As the liquid passes through the heater, the surface of the liquid in contact with the surface of the heater components (molding and / or windings) is heated by conduction, and the remaining volume of the liquid is heated by convection from the liquid to the liquid. along the contact surface. Clearly, the longer the liquid path through the heater, and the higher the temperature of the heater components, more liquid is heated. The components of the heater themselves are heated by a number of different mechanisms: firstly, the molding 5/27 is heated by heating by resistance due to its electrical connection to the secondary winding 6 / 6a / 25 / 25a. Secondly, the molding is also heated by conduction from the adjacent windings - the secondary winding in the case of the preferred embodiment of Fig. 2, and the primary winding in the case of the preferred embodiment of Fig. 3. third, the molding is heated by both heating by parasitic currents and by hysteresis. Fourth, the primary and secondary windings are heated by resistance heating. A control system for the heater is shown in Figures 1 and 4. The objectives of the control system for the heater are, first of all to ensure that the heater supplies water at or near a desired temperature.; and secondly, ensure that the heater can not overheat. Thus, the control system must be able to measure the water outlet temperature from a heater and regulate the power source to the heater depending on the output temperature reading. In addition, the control system must be able to monitor the flow rate of water to the heater to interrupt power to the heater if the flow falls below a certain threshold, or ceases altogether. Although Figure 1 shows a heater having an internal structure of the type shown in Figure 2, the control system shown in Figure 1 can also be used with a heater having the internal structure shown in Figure 3. As shown in FIG. Fig. 1, the inlet mouth of the heater 10 is connected to a water supply pipe 30 via a flow sensor in the form of a flow switch 31. The flow switch 31 is an electromechanical microswitch of the type The flow switch 31 is pre-set to close at a selected flow rate of water through the supply pipe 32. The flow switch 31 is electrically connected to the supply pipe 32. a control panel 33 via a connection 34. The control panel 33 controls the supply of electrical power to the heater. The control parameters of the control panel can be preset by a user within specified limits, using the selector 35 which provides two keypads 36 which can be used to program the control panel 33 to select the desired water temperature delivered by the heater. The selected temperature is displayed in a display 37 mounted adjacent to the keypads 36. The selector 35 is shown next to the control panel 33 but in fact is mounted on the outside of the heater housing, to be accessible by a user. Alternatively, the selector 35 can be omitted altogether, and the control panel 33 simply preset by the manufacturers to deliver water of a particular temperature. The control panel 33 is electrically connected to an electromechanical switch 38 and a solid state relay switch 39, connected in series. The electrical components are connected to the network by a mains connector 40. In order for the heater to operate, the power must be supplied through the mains connection 40 to energize the control panel 33 and the switches 31, 38 and 39; the flow switch 31 must detect an adequate flow of water through the inlet mouth 30; and switches 31, 38 and 39 must be closed. When the heater is started, power must first be supplied as just described and then the flow of water through the inlet 30 is initiated. The desired water outlet temperature is selected by the user, using selector 35; for domestic use, the selected temperature would normally be in the range of 30 degrees centigrade to 50 degrees centigrade. When the flow switch 31 detects a flow rate through the inlet port of the heater 10 which is equal to or greater than a preselected minimum value (e.g. 4 liters per minute) the flow switch 31 closes and after a predetermined delay , reveals that information to the control panel 33, which then closes the switches 38 and 39; this allows the power to be supplied to the primary winding of the heater. As a safety precaution against overheating of the heater, the flow switch 31 must be closed before the switches 38 and 39 can be closed. The switches 38 and 39 are deliberately selected to be of different types and to duplicate the functions among themselves: the switch 38 is an electromechanical switch of known type which is robust and which is designed to disconnect in the event of failure. Nevertheless, because the switch 38 is partially mechanical, it is not adapted to be connected and disconnected constantly, since this would cause excessive wear of the switch. For this reason, once the switch 38 is connected in the game, it remains connected unless the flow switch 31 or the control panel 33 is disconnected. The switch 39 is a solid-state relay of known type, which can be connected and disconnected constantly without deterioration and which therefore can be used for fast power on / off control for controlling the power to the heater. However, switch 39 is a type that tends to fail in the "in" position and for this reason switch 38 is included in the circuit as a precaution against overheating of the heater. The temperature of the water leaving the heater through the outlet mouth 11 is measured by a probe 41 which is located inside the heater adjacent to the outlet mouth 11. The reading from the probe 41 is passed to the control panel. control 33 which operates switch 39 inside or outside, depending on whether the temperature measured by the probe is too low or too high. For domestic purposes, the purpose would be to control the temperature of the mouth water outlet to less than or more than one degree centigrade, although such precise control may not be necessary for all applications. As an additional safety precaution, a circuit breaker switch 42 is mounted on the outer wall of the heater adjacent to the outlet port 11. The circuit breaker 42 is a bimetallic switch and is electrically connected to the control panel 33. The switch 42 is set to open if its temperature exceeds a predetermined maximum (for example 90 degrees Celsius); opening this switch disconnects the control panel 33. Additionally, an additional circuit breaker (not visible) is mounted on the primary winding: this is also electrically connected to the control panel and is set to open if its temperature exceeds a predetermined maximum (eg example 160 degrees centigrade) at which point the control panel is disconnected 33. Once the control panel 33 has been disconnected by one or another circuit breaker, the heater must be completely reset: - all the power must be disconnected and the entire flow of stopped water, to allow the unit to re-establish automatically. The purpose of duplicate and diverse safety measures is to prevent serious overheating of the heater: - the heater could explode like a pump if it were sufficiently overheated, and it is necessary to take precautions against not only failure or malfunction of one or more of the security switches, but also the mistreatment of the heater by a user. In the event of a power failure, when the power is restored the water temperature is automatically restored to a safe temperature, for example, 35 degrees Celsius. Water can continue to flow through the heater while the power is disconnected, such that in an emergency, the water passed through the heater can still be used, although it will of course be not heated. The control system just described can be modified by replacing selector 35 and control panel 33 with a thermostat of known type. In this case, the user would select the desired temperature simply by setting the thermostat dial. This modified control system would not give such exact temperature control as the system described with reference to Figure 4, but would be cheaper to manufacture.The efficiency to be expected from the heater of the present invention may vary with the size of the heater and the outlet water temperature range, however, by way of example, a 13 kW heater according to the present invention, constructed and prefixed as described with reference to Figs. 1, 2 and 4 above, has an efficiency of 99 percent with a power fatPtor of 0.93 The heater of the present invention is designed to operate satisfactorily with a wide range of flow rates, so that it can operate over a wide range of water pressures. in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it refers.