GB2147979A - Liquid heater - Google Patents

Abstract

The heater comprises a tank 10 containing an electric heater 16. The tank 10 is charged with water through a valve 32 controlled by a float 28 which maintains a predetermined water level. A vent opening 30 maintains the water in the tank at atmospheric pressure. The charge of water is maintained at an elevated temperature by a heater 16 having a thermostat 40. Cold water is fed through an inlet 21 to a coil 18 in the tank 10 and is heated by the water in the tank 10 as it flows through the coil to an outlet 23. In a modified heater (Figs. 7 to 9) the float 28 and valve 32 are replaced by an electric level sensor 160 which operates a solenoid valve 166. The sensor 160 controls LEDs 170 which indicate when the heater is on, off, filling or overheating and when the water level is too high or too low. <IMAGE>

Description

SPECIFICATION Heater This invention relates to heaters for liquids, for example electric hot water heaters.

Known types of electric water heaters in clude:- (1) Closed water heaters which are designed to work under the pressure of the water supply mains, the flow of water being controlled by one or more valves in the outlet system. These heaters have the disadvantages that safety devices, for example a cold expansion valve, a temperature and pressure relief valve, and a limiting valve have to be incorporated for safe operation of this type of water heater. At the present time, this type of water heater does not meet certain safety requirements and the use of the safety valves is not accepted and approved in various places including Hong Kong.

(2) Cistern-fed water heaters supplied from a feed cistern, in which the flow of water is controlled by one or more valves in the outlet system and so arranged that the expanded water can return to the cistern. This type of water heater is not suitable for installation in high-rise buildings the construction of which is not intended for the provision of the necessary vent pipes. The installation of vent pipes in these buildings can be very costly and it is inconvenient to have the numerous vent pipes needed when every household in the building requires the installation of such an electric water heater. In addition these water heaters are not suitable for areas where the supply of water is from mains rather than from the cistern.

(3) Open-outlet water heaters in which the flow of water is controlled by a valve in the inlet pipe and so arranged that the expanded water can overflow through the outlet pipe.

These heaters are capable only of single-point use supplying a limited volume of hot water.

For industrial or technical institutions, or domestic units requiring bulk hot water supply and multi-point outlets, this water heater cannot cannot meet the requirements of the consumer.

(4) Cistern-type water heaters having feed cisterns as integral parts of the appliance. This type of water heater does not have the required pressure for a shower because the feed head is less than 4 p.s.i. It therefore is suitable for bath purposes only, when the electricity and water consumption will greatly exceed that of a shower. As the water pressure is very different at the cold water and the hot water outlets, the cold water cannot be mixed well with the hot water and this results in inconsistent water temperatures.

The present invention provides an apparatus for heating liquids, the apparatus comprisng a vessel for charging with a heat transfer liquid, means for heating heat transfer liquid charged to the vessel, and a conduit for passing liquid to be heated through the vessel in heatreceiving relationship with heat transfer liquid and/or the vapour thereof in the vessel, the vessel having vent means for maintaining the interior of the vessel at atmospheric pressure during use.

Conveniently, the heat transfer liquid and the liquid to be heated are both water but this is not necessarily so.

The apparatus advantageously includes means for maintaining a predetermined working level of heat transfer liquid in the vessel, these means may comprise a float positioned in the vessel and operating an inlet valve but, advantageously, the level-maintaining means comprises electrical sensing means responsive to liquid in the vessel falling below the predetermined working level to open an inlet valve for the heat transfer liquid. Preferably the sensing means are responsive to liquid in the vessel rising to a second predetermined level higher than the working level to close the inlet valve.

Conveniently, when the heat transfer liquid and the liquid to be heated are the same, the inlet valve is also connected to the source of the liquid to be heated.

When the liquid is to be heated solely by heat transfer from heat transfer liquid, the conduit is located entirely below the predetermined working level. In other cases, the working level is below the top of the coil and the liquid is then heated, at least in part, by heat transfer from the vapour of the heat transfer liquid.

Embodiments of the invention may include sensing means, conveniently electrical, responsive to the level of liquid in the vessel rising to a predetermined overflow level to actuate an alarm or indicator device and/or sensing means, again conveniently electrical, responsive to the level of liquid in the vessel falling to a predetermined minimum level to deactivate the heating means.

Preferably, the electrical sensing means comprise at least two conducting rods terminating at respective different levels in the vessel, one rod being an electrically-common rod and the sensing means being responsive to the formation of an electrical circuit between that rod and the or each other rod. In other embodiments, the wall of the vessel is electrically-conducting and the common connection made through it.

The heating means conveniently comprises an electric heating element and is preferably thermostatically controlled so that the heat transfer liquid charged to the vessel is maintained at a predetermined, and preferably selectively variable, temperature The conduit is conveniently provided by a coil of tubing of, for example copper. The coil may, at least in part, surround the heating means.

In another aspect, the invention also provides a method of heating a liquid, in which a vessel vented to the atmosphere is charged with a heat transfer liquid, the charge of liquid in the vessel is heated, and liquid to be heated is fed in heat receiving relationship but without mixing through the heated liquid and/ or the vapour thereof in the vessel.

In use, the vessel of a heater according to the invention will normally be maintained charged with the heat transfer liquid at a predetermined temperature. Since the heating means will usually be located within the vessel, substantially the whole of its exterior can be lagged in thermally-insulating material. The heater will therefore supply heated liquid whenever flow through the conduit is produced, for example by opening a tap in a pipe connected to the outlet of the conduit, and will supply the heated liquid continuously provided that the water flow rate and heating power of the heating means are chosen appro priately.

Heaters according to the present invention can work well over a range of water supply systems and at various water pressures. The heater can be connected directly to the mains or to a cistern supply. Water storage tanks, vent pipe leading to expansion tanks and additional safety devices are not required. The hot water outlet can be connected for multipoint use and capable of simultaneous hot water supply to various outlets at different places. The temperature of the hot water can be substantially constant under normal working conditions and no dangerously high temperature will be generated. In case of failure, any excess water, pressure or steam can escape through the vent means, the outer end of which can be situated on the outside casing of the water heater.

It is important to note that the interior of the vessel is maintained constantly at atmospheric pressure, thus constituting an important safety feature and distinguishing the heater of the invention from water-heating apparatus in which water is heated in a tank with an expansion space but without a vent to the atmosphere and fed from an elevated supply cistern.

Two embodiments of the invention will now be described by way of example with reference to the drawings, in which: Figure 1 is a vertical sectional view of a vertical wall mounting electric water heater.

Figure 2 is a horizontal sectional view on the line A-A of Fig. 1, Figure 3 is a horizontal sectional view on the line B-B of Fig. 1, Figure 4 is a top view on the line C-C of the heater of Fig. 1, Figure 5 is a bottom view on the line D-D of the heater of Fig. 1, Figure 6 is a front view of the heater of Fig.

1, Figure 7 is a somewhat schematic vertical sectional view of a free-standing electric water heater, Figure 8 is a somewhat schematic elevational view of an inner tank of the heater of Fig. 7, and Figure 9 is a wiring diagram of an electrical control system of the heater of Figs. 7 and 8 The heater comprises a tank 10 constructed of metal, for example stainless steel sheet or copper, and having a side wall 11, a top cover 35 and a domed bottom 1 3. The diameter can be from about 30 to 70 cm and the height a maximum of about 180 cm.

The tank is mounted in a housing 14 having a floor 38 and a top cover 33. Removable panels 39. 34 in the floor 38 and top cover 33 allow access to in interior of the housing 14. A removable panel 1 2 of the top cover 35 of the tank 10 allows access to the interior of the tank. The space between the housing 1 4 and the tank 10 is thermally insulated by heat insulating material, for example fibre glass 15. The housing 14 has brackets 41 (Figs. 2 to 5) for attachment of the heater to a wall, floor or other convenient structure.

An electric heating element 1 6 is fitted through an aperture in the bottom 1 3 of the tank 10 and includes a pocket 1 7 for a thermostat sensor and a pocket 37 for a thermal cut-out sensor. The pockets enclose a thermostat 40 and a thermal cut-out 1 9 respectively to allow the element 1 6 to maintain water in the tank 10 at a predetermined temperature. The thermostat 40 is connected to a control 42 on the exterior of the housing 14 and the thermal cut-out 1 9 to a control on the interior of the housing 14. The controls thus allow adjustment of the thermostat 40 and the thermal cut-out 19. An indicator light 43 is fitted to the exterior of the housing floor 38.

A coil 1 8 of 1 cm diameter copper pipe is mounted inside the tank 10 by fixing flanges 36. An inlet pipe 20 and an outlet pipe 22 pass through the side wall 11 of the tank 10 and thence extend vertically to pass through a floor 38 of the housing 14. The inlet and outlet pipes 20, 22 terminate outside the housing 14 at suitable connecting unions 21, 23. A drain-off value 24 closed by a drain plug 25 is fitted to the lower surface of the tank 10.

Within the housing 14 but externally of the tank 10, the inlet pipe 20 is secured by a bracket 16 and passes through the side wall 11 of the tank 10 at a union 27 sealed through the side wall. The inlet pipe 20 is connected internally of the tank 10 to a Tjunction 31, one limb of which supplies water to the tank 10 through a float valve 32, the other limb of which is connected to the copper coil 18.

The float valve 32 is operated by a floating ball 28 on an arm 29 inside the tank 10. The ball 28 and the float valve 32 thus maintain a predetermined level of heat transfer water in the tank 10. An overflow 30 vents the interior of the tank 10 to the atmosphere and also allows water to escape from the tank 10 in the event of malfunction of the float valve 32 or ball 28. The water in the tank 10 is therefore maintained constantly at atmospheric pressure.

For use, the heater is mounted by means of its mounting brackets 41 and the inlet union 21 is connected to a source of cold water, for example a cold water main or the output pipe of a storage tank. The outlet union 23 is connected to one or more hot water points, for example hot water taps or a shower apparatus. The heating element is connected via a switch or protective devices to a suitable electrical power source and its thermostatic device 40 adjusted by means of the control 42 to a setting appropriate to a desired hot water temperature.

When the cold water source is turned on, water flows through the inlet 20, the Tjunction 31 and the float valve 28 to charge the tank 10 with water which is to be heated and which will, in use of the heater. transfer heat from the element 1 6 to the water in the coil 18. When the water level in the tank 10 determined by the adjustment of the ball 28 and float valve 32 is reached, the float valve 32 closes and flow of water into the tank 10 through the float valve 32 stops. During further use, the water level in the tank 10 is maintained by operation of the ball 28 and float valve 32.

The heating element 1 6 is now supplied with power to heat the water in the tank 10 to the temperature determined by the setting of the thermostat 40. When the water in tank 10 reaches the predetermined temperature, for example 85"C, the heater can be used to supply hot water. Opening of a tap or other valve of an apparatus connected to the outlet union 23 allows water to flow through the coil 1 8 in heat-receiving relationship with the heated water in the tank 10. The heated water emerges from the outlet union 23 and flows to the taps or other apparatus at which it is required.Once the water in the tank 10 has reached its operating temperature, the heater can provide hot water instantaneously and supply hot water continuously, provided that the flow rate of water through the coil 1 8 and the power rating of the heater are chosen appropriately.

The heater has the advantage that failure of the cold water supply is immediately evident because it results immediately in it not being possible to withdraw hot water from the heater. In the event of such failure, the heater 1 6 will remain in a safe condition since it will continue to be immersed in the water in the tank 10. Loss of water by evaporation will be very slow because water vapour will tend to condense on the inner surface of the top cover 35 of the tank and then run back into the lower part of the tank 1 0. It should also be noted that when the tank is empty, the heating element 1 6 is spaced from the coil 1 8 by a large, insulating air gap. A further safety feature of the heater is that the tank 10 is unpressurised.

Heaters embodying the present invention can of course be made in a wide range of water capacities, for example from a few litres to several hundred litres. The electrical power can range from for example, 3 kW to 36kW.

Figs. 7 to 9 of the drawings show a freestanding electric water heater embodying the invention. The heater includes a tank 110, of stainless steel or copper, having a domed bottom 11 3 with a drain cock 1 24. A removable cover 1 35 closes the top of the tank 110 and supports a water level sensing device 1 60 described in more detail below. The tank 110 also has a suitably-positioned overflow and vent opening 1 30 which ensures that the contents of the tank are maintained permanently at atmospheric pressure. An electric heating element 11 6 protrudes through an aperture in the side of the tank 110.The heating element 11 6 has a thermostat sensor and a thermal cut-out sensor similar to those fitted to the element 1 6 of the embodiment of Figs. 1 to 6.

The tank 110 is enclosed by an enamelled steel housing 11 4 and is supported by legs 141 protruding through a floor 1 38 of the housing from the domed bottom 11 3 of the tank 11 0. A removable panel 1 34 in a top 1 33 of the housing 11 4 allows access to be gained to the level-sensing device 1 60. The space between the housing 11 4 and the tank 110 is filled with heat insulating material (not shown), such as fibre glass.

A coil 11 8 of copper tube is mounted inside the tank 11 0. The coil 11 8 is connected at one end to a pipe 1 20 (see Fig. 8) positioned between the housing 11 4 and the tank 110. A further pipe 162 leads to a charging inlet 1 64 of the tank 110 and contains a solenoid-operated valve 1 66. The pipes 1 20 and 1 62 are connected to a common inlet union 1 21 of the water heater. The other end of the coil 11 8 is connected by a pipe (not shown) to an outlet union (also not shown) of the heater.

The water level sensing device 1 60 comprises five stainless steel rods 1 60a, 160b, 1 60c, 1 60d, 1 60e of decreasing length which are electrically insulated from each other and protrude into the tank 110 to five respective different predetermined depths.

The longest rod 160a is "common" and electrical connections can be made by water in the tank 110 between this rod and each of the four shorter rods 160b to 160e. The sensing device 1 60 gives an electrical output signal which is indicative of which of the four shorter rods is/are in electrical communication through water in the tank 110 with the longest rod 160a. The sensing device 1 60 is preferably supplied with alternating current to avoid electrolysis of the water in the tank 110.

The second largest rod 160b protrudes into the tank 110 to a depth that is considered to be the lowest safe level of water in the tank.

Rods 1 60c and 1 60d protrude respectively to the minimum and maximum normal operating levels of the water, whilst the shortest rod 1 60e protrudes to a depth slightly below the level of the overflow and vent opening 1 30.

The electrical output from the sensing device 1 60 is fed to a printed circuit board 1 68 (see Fig. 9) which has a series of LED indicators 1 70. The circuit board 1 68 is housed in a control box 1 72 mounted on the exterior of the housing 114 (see Fig. 7), the LED indicators 1 70 being incorporated, together with a temperature control for the thermostat of the heating element 11 6, into a control panel on the front surface of the control box 1 72. In a modified embodiment, the control box 1 72 is mounted remote from the heater and connected thereto by a suitable cable.

Fig. 9 shows the electrical circuits of the heater. A power connector 1 80 allows the heater to be connected to the mains and is itself connected to a heating circuit containing a temperature limiter 182 connected to the cut-out sensor mentioned above, a contactor 184, a thermostat 1 86 connected to the thermostat sensor mentioned above and the heating element 11 6. The printed circuit board 1 68 derives its power from the power connector 100 by way of a cable 1 87 and a step-down transformer 1 88. The solenoid-operated valve 166 and temperature limiter 1 82 are also connected to the circuit board 168.

The printed circuit board 1 68 carries a control circuit arranged to process the electrical output from the sensing device 1 60 and to control the solenoid valve 1 66 and the LED indicators 1 70. In normal operation. when the sensing device output indicates that the water level in the tank 110 is below the minimum normal operating level, as detected by the rod 160c, the control circuit on the board 1 68 causes actuation of the solenoid valve 1 66 and water is admitted to the tank through the pipe 1 62 and inlet 164. When the water level has risen to the maximum normal operating level, the solenoid valve 1 66 is closed in response to a signal from the rod 160d.

Whilst the valve 1 66 is open, an LED indicator designated "REFILLING" is arranged to light up.

If, for example because of malfunction of the valve 166, the water level should rise above the maximum normal operating level, a signal derived from the output of the shortest rod 1 60e of the sensing device 1 60 will cause an LED indicator designated "HIGH LEVEL ALARM" to be illuminated. Similarly, if the water level should fall below the depth to which the second longest rod 1 6Ob protrudes into the tank 110, for example because of failure of the water supply, a "LOW LEVEL ALARM'' LED is illuminated and the temperature limiter 1 82 actuated to interrupt the supply of power to the heating element 11 6.

The remainder of the LEDs are arranged to indicate "POWER ON", "POWER OFF" and ''OVERHEAT''. the latter when the temperature limiter 1 82 switches the heating element 11 6 off when the temperature of water in the tank 110 rises above a predetermined maximum.

It will now be seen that the water heater of Figs. 7 to 9 functions identically to the heater of Figs. 1 to 6, except for the manner by which the level of water in the tank is maintained. Many features of the two embodiments described may of course be interchanged independently between the two heaters.

In a further modified heater, the water level in the tank is arranged to be below the top of the coil and, in this heater, the water passing through the coil is heated, at least in part, by steam surrounding the coil and produced by heating the water in the tank.

Claims (14)

1. An apparatus for heating liquids. the apparatus comprising a vessel for charging with a heat transfer liquid, means for heating heat transfer liquid charged to the vessel, and a conduit for passing liquid to be heated through the vessel in heat-receiving relationship with heat transfer liquid and/or the vapour thereof in the vessel, the vessel having vent means for maintaining the interior of the vessel at atmospheric pressure during use.

2. An apparatus according to claim 1, including means for maintaining a predetermined working level of heat transfer liquid in the vessel.

3. An apparatus according to claim 2, in which the level-maintaining means comprise a float positioned within the vessel and operating an inlet valve for the heater transfer liquid.

4. An apparatus according to claim 2, in which the level-maintaining means comprise electrical sensing means responsive to liquid in the vessel falling below the predetermined working level to open an inlet valve for the heat transfer liquid.

5. An apparatus according to any one of claims 2 to 4, in which the conduit is located substantially entirely below the predetermined working level.

6. An apparatus according to claim 4, in which the sensing means are responsive to liquid in the vessel rising to a second predetermined level higher than the working level to close the inlet valve.

7. An apparatus according to any preceding claim, comprising sensing means responsive to the level of liquid in the vessel rising to a predetermined overflow level to actuate an alarm or indicator device.

8. An apparatus according to any preceding claim, comprising sensing means responsive to the level of liquid in the vessel falling to a predetermined minimum level to deactivate the heating means.

9. An apparatus according to claim 7 or 8, in which the sensing means are electrical.

10. An apparatus according to any of claims 4, 6 and 9, in which the electrical sensing means comprise at least two conducting rods terminating at respective different levels in the vessel, one rod being an electrically-common rod and the sensing means being responsive to the formation of an electrical circuit between that rod and the or each other rod.

11. An apparatus according to any preceding claim, having a common inlet for charging heat transfer liquid to the vessel and supplying liquid to be heated to the conduit.

12. An apparatus according to claim 11, in which the inlet valve and the conduit are connected to a common inlet of the apparatus.

13. An apparatus according to any preceding claim, in which the heating means comprises an electric heating element.

14. An apparatus according to any preceding claim, in which the conduit comprises a coiled tube within the vessel.

1 5. A method of heating a liquid, in which a vessel vented to the atmosphere is charged with a heat transfer liquid, the charge of liquid in the vessel is heated, and liquid to be heated is fed in heat receiving relationship but without mixing through the heated liquid and/or the vapour thereof in the vessel.

1 6. A method according to claim 15, in which the heat transfer liquid and the liquid which is heated are both water.

1 7. An apparatus for heating liquids, substantially as hereinbefore described with reference to Figs. 1 to 6 or Figs. 7 to 9 of the drawings.

1 8. A method of heating liquids, substantially as hereinbefore described with reference to the drawings.