This invention relates to apparatus for heating -water for domestic or commercial purposes and being provided with supply of vatβr, for example, cold water under pressure from a water main.

Hot water supplies are usually provided from a tank or otiaer- storage container, in which there is heating means such as an electrical immersion heater or a coil through which, hot water heated by a boiler is circulated. Heat ^* exchange by such methods is relatively slow and inef icient ^* ., due to gassi ication., i. . water bubbles adhering ^* to the heater element, and also the- storage of "he hot water is wasteful._

There- have therefore been proposed various electrical heating devices which have efficiency sufficient to heat water as it- lows through the apparatus.. This arrangment. ^" eliminates- the need, for- storage of ho water. T e- e-lectrical heating is. by- means of electrical, resistance heaters- which, are usually coiled wires disposed in the water- passage. This type of apparatus is however only capable of producing a small flow of hot water ^* , for example being sufficient to supply only one tap at a time.

It is the object of the invention to provide water heating apparatus having no necessity for storage of the water which has been heated and which has a high efficiency for -e conversion of electrical energy into heat.

According to the invention there is provided water heating apparatus comprising an inlet duct, an outlet duct, and a water heating unit between the inlet and outlet ducts, τhe heading unit including a printed circuit hearer means.

y- , w L

The invention will now be described by way of example with reference .to the accompanying drawings in which;

Figure 1 is a schematic perspective view of a water heating apparatus constructed in accordance with one embodiment of the invention,

Figure 2 is a perspective view of a body forming part of the water heating apparatus,

Figure 3 Is ~- further, schematic, perspective view of the body of the water heating apparatus, showing the inside thereof, with an inlet pipe and heater -unit therein,

Figure is a perspective view of the inlet pipe and heater unit of Figure 3 _s removed from the body,

Figure 5 is a end view of the spiral heating unit,

Figure 6 is a schematic perspective view .of a first embodiment of water heatin means using the body of Figure 3, together- with electrical control means,

Figure 7 is a schematic perspective view similar to Figure 6 of a second embodiment,

Figure 8 shows an arrangment of a three stage water heating apparatus, together with control means,

Figure 9 shows a heating unit arrangement where temperature sensors are built in with the heating elements,

Figure 10 is a circuit- diagram of the control of the apparatus,

Figure 11 is a cross-sectional view ^* of an inlet section of another embodiment of the invention,

5 Figure 11a_ is a perspective view of an alternative heater unit for use with the inlet section of Figure 11,

Figure 11b. is a cross—sectional view of an outlet section of the embodiment of Figure 11 ,

Figure 12 is a perspective view of a further alternative ^" O heater unit ,

Figure 13 is a scJaematic perspective view of a still further alternative heater unit,

Figure ^ is a lay-out of a yet still further form of water heating apparatus,

^" *5 Figure 15 is a cross-sectional view of a still different form of the apparatus ^' , and

Figure 16 is a diagrammatic lay—out of the apparatus in Figure 15.

Referring ^* to Figure 1 this shows a water heating 20 apparatus for use for example in a domestic situation for providing a supply of hot water and being supplied from a cold water main supply.

The apparatus as shown in i.gure 1 includes an inlet section 10 and an outlet section 11 and a body ^■ ~5 section 12, containing the heating means of the appliance, situated between the inlet and outlet sections. Part of the casing has been removed for clarity and it is to be

- - -

understood that the external shape of the apparatus may take any other form instead of the generally rectangular configuration shdwn. In addition the body section 12 can also be other than rectangular,for example it can be of pear-shaped cross-section, as shown in Figures 2 and 3«

On the inlet section 10 there can be mounted a control 13 by means of which the temperature of the water delivered can be- regulated, as will be described.

Figures 2 to 5 show the construction and arrangement o.f various parts of a first embodiment of water apparatus, to fit into a casing in the form of Figure 1 or in any suitable alternative form.

Figures 2 and 3 show a metallic body 1^ of generally pear shape in transverse cross—section. The body has end walls 15 ^" , 16 respectively and in the end wall 15 _» which is the inlet end of the body, .there is provided a generally central hole 17- The hole 17 is thr«aded to receive an adaptor plug supporting a cold water inlet pipe 18 which, in use, is arranged to receive pressurised cold or relat- ively cold water from, for example, the main supply.

If required the inlet could incorporate a non—return valve. The wall 1 also contains a further threaded hole 19, which is plugged, in use, and a slot 20.

The end wall 16 has a hole 21, longitudinally aligned with the hole 19, and which is threaded like the hole 17, to receive an adaptor plug 23 (Figures 6 and 7), similar to that fi-fcted in the hole 17, and carrying an outlet pipe 2 .

The inlet pipe 18 extends to the interior surface of the end wall 16 where it is closed. However the pipe 18 has an axially extending slot 2 in its surface to allow the cold water to flow therefrom into a spirally arranged heater unit 26 shown in Figure 3«

The heater unit, shown best in Figures and 5, is in the form of an electrical printed circuit heater 2 sandwiched between a pair of metal plates and rolled into a iral. Connections 28 for supplying power to and for controlling the heater are provided on a longitudinal extension part at one corner of the heater unit which protrudes through the slot ^* 20. A glass or metal laminate, i.e. aluminium can be provided around the outside of the heater unit.

With the heater unit fitted in the water heating body 1 and being closed by the end walls 1 » 16, which are,for example, secured to the remainder of the body by welding as shown in Figure 3 _. it can be appreciated that cold water entering the inlet pipe 18 will _0ow out o th slot 25 and into th innermost -turn of the φiral of' the heater -unit.. The water will then ^' flow around the remaining spirals until it leaves the outermost part of the spiral and flows out of the outlet pipe 2 carried by the plug 23 fitted in the hole 21 in the outlet end wall 16 of the body 14.

The fact that the heater nnit is a spiral, in this example of four turns, means that the surface area of the heater unit contacted by the water, as well as the contact time is signincantly increased as compared to conventional heater units such as heating coils. This increases the efficiency of the heater, whilst enabling it to be kept relatively short and compact, thus allowing the water heating apparatus itself to be made compactly and less expensively. It has also been found that this construction

of heater substantially reduces gassifica ion, further improving the heating -ef_g.ciency.

Figure 6 shows a first example of an assembled body 14, inlet and outlet pipes 18, 24 heater unit 26 and associated controls for water heating apparatus of the invention. A casing 30 is shown schematically around the body 14, and this can contain asbestos or the like as heat insulation material. Electrical connection lines 31, 32 are taken from a power supply (to be described in Figure 10) to the connections 28 on the corner extension 29 of the heater unit. An override or cut-out sensor 33 is fitted on the body 14 to monitor the temperature of the water entering the outlet pipe 24 and to operate if a predetermined maximum value is exceeded. For example it could operate to switch off the heater unit and could be manually or automatically reset. Electrical lines 34, 35 connect the sensor to a control circuit, not shown.

Figure- 7 shows a similar arrangement to figure 6, but with an increased number of printed circuit heaters, giving six contacts 36 and associated supply _ϋnes 37- As well as an override sensor 38, similar to the sensor 33 in. Figure 6, there are additional sensors 39, 40 in the inlet and outlet pipes 18, 24 respectively, to provide electrical signals related to the temperature of water flowing therein. Each sensor has a pair of electrical connection lines leading therefrom to the control means of the water heating apparatus, which will be described below.

"Typically a small heater unit, such as that shown in Figure 6, will be used in a 5kw water heating apparatus and a multi-circuit arrangement such as in Figure 7 would produce 10kw.

O PI

Figure 8 shows the use of three body assemblies of Figure 6 connected in series, so that each one can perform a stage of the water heating operation. The inlet pipe 18 of the first body assembly is fed from the cold water supply and after being heated by passing around the spiral heating unit in the body, the water passes out through the outlet pipe 24 of said first body, which also serves as the inlet pipe to the next body downstream in the series, and so on for the third and any subsequent body assemblies, as the number is not limited to the three shown. This- arrangement reduces the wear on each heater unit and thus prolongs the life thereof. Each body assembly is shown as in Figure 6, but with a water tempera¬ ture- sensor 41 , and although not shown each body assembly can also be provided with an override sensor. A heater control unit 42 and a temperature control unit 3 are also shown, along ^* with a water outlet distribution system, of five outlet' branches 44 for ^* the heated water to be taken off. The temperature sensors monitor water tempera— ture along the whole body assembly and can detect, hot or cold spots, for example, to cut out the heater in one particular section thereof. Thus with this arrangement each assembly can raise the water temperature by a given amount so that the heating load is φread over three heater units to produce water of the required temperature at the outlet of the end assembly. If required the bodies could be as in Figure 7«

Figure 9 shows an arrangement where the temperature sensor 44 is produced together with the heating elements 45 in the printed circuit board of the heater unit. This is a particularly compact arrangement allowing connections 46 to be made to the heater control unit 47 and connections 48 to the temperature control unit 49 at the board edge, thereby dispensing with an external, separate temperature sensor, like the sensor 41 in Figure 8. However like the sensor 41 , the sensor 44 monitors water temperature along

the whole of the heater unit and can cut out a heating section if a hot spot is detected.

Figure 10 shows an electrical control circuit suitable for all the water heating arrangements shown in Figures 1 to 9, where the heating apparatus has associated temperature sensing.

A spiral heater unit is denoted by the numeral 50 a d sensors for monitoring inlet and outlet water temperature are denoted by the numerals 39 and 40, as for Figure 7, in the inlet, and outlet sections 10 and 11. The heater unit is controlled through a solid state switch or relay 31. This is provided with a mains electriαal supply at

52. If a relay is used, it can be of any suitable type, for example incorporating- a triac value.

The sensors 39, ^0 are connected in a bridge circuit 53 which is variable at 54 to regulate the heater unit output. This variation is carried out by way of the control knob 13 of Figure 1. - A 24 volt power supply is connected between lines 55 and 5^> with the voltage being supplied to the switch or relay 5 • The line 55 is continued to the variable adjustment means 54 of the bridge circuit

53 _. whilst the line 56 is connected to the opposite point of the circuit 53« -^ line 57 extends from a further junction of the bridge circuit between the connection of the sensor 39 and a resistor to one input of an operational amplifier 58. This is a (temperature) difference amplifier. A line 59 extends from the remaining junction of the circuit 53 to another input of the amplifier 58. An output line 6θ from the amplifier is connected to the line 5 of zero voltage, through resistors 61 and 62. Connected between the lines 59 and 60 is a coil 63.

A line 63 extends from the switch or relay 51 to join the line 60 between the resistors 61 , 62. It has a diode

64 connected in it between collector and base and a line

65 from the emitter of the diode 64 extends to the base of another diode 66, whose collector and emitter are in a line 67 between lines and 63. A further resistor 68 is connected between the lines 56 and 65 to complete the circuit.

The arrangement is such that the inlet and outlet temperatures are sensed by senors 39, 40 and according to the setting of the- control knob 13 at variable adjustment 54, the heater current is regulated to maintain the chosen output" temperature despite changes in input temperature.

Referring to Figures 11, 11a. and 11t), these show inlet and outlet ^* sections and an alternative form of heater unit for use in water heating apparatus in the form shown in Figure 1. ^* The inlet section 10 shown in Figure 11 includes a central water duct 114. In the entrance of this is an adaptor- 115 for attachment to associated pipework and this also incorporates a non—return valve indicated generally at 116. The- on-return valve may take any conventional form. Extending into the duct 114 in the inleir section is an electrical temperature sensor device 117 which is capable of providing an electrical signal related to the temperature of the water flowing through the inlet duct.

Surrounding the duct 114 are casings containing the electrical supply and control equipment can be of the firms already described. The provision of these- around the inlet duct provides for the cold water flowing there¬ through cooling for the electrical and electronic equipment.

At the top of the section 10 there is a screw adaptor 118.

The outlet section 11 also has a central duct 119 through which the heated water flows. At the outlet end is an adaptor 120 for connection to associated pipework and there is also an electrical temperature sensor 121 which extends into the duct 119- There is also a screwed adaptor 122 at the inlet end of the duct 119.

Situated close to the duct 119 is a temperature responsive switch 123. Like the sensors 33 and 38 already described,, this is arranged to operate in the event tha ^* t the temperature in ^' the outlet duct 119 exceeds a predetermined maximum value. It is arranged to be manually reset when it has been actuated in the event of excess temperature conditions.

As shown in Figure 1, the body section 12 can be. in the form of ^* a rectangular cowling, and within this is a cylindrical heating unit 124 shown in Figure 11a. This has screw threaded ends to engage in the adaptors 118 and 122 in the inlet and outlet sections 10 and 11. ¥ithin this is a matrix indicated at 125 made up from a number of printed circuit boards each with printed electrical heater circuits on their respective surfaces. The matrix is made up from a number of boards arranged perpendicularly to one another so as to define a number of square or rectangular through flow passages for water each passage being bordered by the heating elements printed on the circuit boards.

Conveniently the matrix is made up from a number of flat boards with slits which enable inter—engagement between the boards in a rigid manner. Electrical connections between them are either at the ends or at any convenient place within the matrix.. ^'

External connections of which there are four shown at 126 provide electrical supply to the printed circuit boards.

The apparatus therefore operates with water flowing - 5 through the inlet duct 114 ofthe- inlet section 10 and through the matrix 125 to be heated as it passes through this unit. The water having been heated then flows out through the outlet duct 119« Heating of ihe water occurs only when there is a demand and there is therefore no 10 necessity for storage of heated water.

Although this matrix type of heater unit is quite satisfactory in use, it is more expensive than the spiral type of heater unit and provides a shorter travel than with the sprial type.

15 Figure 12 shows a further alternative heater unit having a number of parallel printed circuit board plates 134.- Each is rectangular and they are mounted apart by support columns 135. Such a unit would be enclosed within a surrounding cowling and electrical connections

20 can be- made at the edges of the plates.

Figure 13 shows an alternative matrix form of heater unit at 137 of generally rectangular configuration instead of the cylindrical form shown in Figure 1 la.. It is however constructed in similar manner. Part is broken away for 25 clarity to show the heating elements.

Figure 14 shows an alternative heating apparatus which includes a casing 138 containing a hollow body 139- An inlet pipe l4θ and an outlet pipe 141 are connected to opposite ends of the body 139 and within it are a 30 pair of printed circuit board heater plates 142 having provision for electrical connection of their opposite ends outside the body 139- These may be arranged to

provide disturbance to the fbw of water through the body so that maximum heat exchange takes place from the heaters to the ^" water. The inlet and outlet pipes 140, 141 include respective temperature sensors 143, 144 connected in control circuits in the manner already described.

The inlet pipe 140 is connected to pipework 145 which includes a mannual valve 146 for interrupting the supply and. a solenoid operated valve 1 7 upstream of the manual valve. The solenoid valve is connected in the control circuit to regulate the supply according to the load and output temperature requirements.

Figures 15 and 16 shows a further form of water heating apparatus which might be used in a commercial environment. A number of alternative sections are shown of which two or more- may be used in combination, or each can be used individually as required. Inlet and outlet sections are omitted and. there is shown only the heating unit which, in this- example, has four sections. The firs ^* t section 148 nas a tubular printed circuit board heater 1 9 being flared towards the inlet end.. Figure 16 shows the circular section of this. The printed heater elements are shown as a coil on the printed circuit board and electrical connections to opposite ends of this are indicated at 150.

A similar but cylindrical form of heater unit 151 is shown in the section 15 at the opposite end of the appliance. Electrical connections to this 'are indicated at T53.

The section 15^ has two parallel cylindrical units each formed as a printed circuit board 155, 156 ^" . Respective electrical connections are indicated at 157, 158.

The further form showri. ^" in the section 159 has three parallel cylindrical units 160, 161, 162 with respective electrical connections 163, 164, 165.

Other forms of heater can be used each incorporating printed circuit boards. These may be insulated or exposed directly to the water in which case adequate earthing is necessary.

As stated, however, the spiral arrangement is most advantageous, since in addition to its efficiency advantages and lower cost, it simplies electrical connections thereto because they can be made at any convenient place.

¥ith some constructions of water heating apparatus using this invention, it is envisaged that it will be possible to reduce costs to a degree where the apparatus can be considered disposable.