AU652309B2

AU652309B2 - Control unit for electrically boosted solar hot water systems

Info

Publication number: AU652309B2
Application number: AU32126/93A
Authority: AU
Inventors: Alan Collier Edwards
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-02-03
Filing date: 1993-01-29
Publication date: 1994-08-18
Anticipated expiration: 2013-01-29
Also published as: AU3212693A

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION f'or a Standard Patent OR IGIN AL NAME OF- APPLICANT: ALAN COLLIER EDWARDS ACTUAL INVENTOR: ADDRESS FOR SERVICE: ALAN COLLIER EDWARDS 44 44 44 o 4 4 4 4~ o 4 4. Og o 4 4 4 4 i.

en, 0 4 4 4 57 BIRDWOOD PARADE DALKEIT-, W.A. 6009- INVENTION TITLE: CONTROL UNIT FOR ELECTRICALLY BOOSTED SOLAR 1-OT1 WATER SYSTEMS DE TAILS OF ASiSOCIATLID I11OVISIONAL APPLICATIONS Nos.

APPLICATION No. 13L-0063/92 3rd.February 1992 Thie following Statement is a 111ll description of' this invention, including the best method of' perl'orming it kniowni to mie:- 2 This invention relates to a control circuit for electrically boosted solar hot water systems.

Most electrically boosted solar hot water systems are generally provided with a thermally responsive normally open low temperature switch which closes when the temperature of the water falls below a predetermined lower limit and automatically re-opens when the temperature rises above the predetermined limit; and (ii) a thermally responsive normally closed over temperature switch which opens when the temperature of the water exceeds a predetermined upper limit and which can only be returned to the normally closed position by the operation of a reset button.

With such an arrangement if the water is heated to over the predetermined upper temperature limit by solar radiation, as would be the case when there is no draw on the unit for a period of several days in the hot summer period, the over temperature switch will open and remain open.

When electric boosting is required it is necessary for the householder to climb onto the roof and operate the reset button. If the over temperature switch is replaced by an automatically resetting type of switch *o00 0 to obviate the necessity for the householder to climb onto the roof to 00 20 reset the switch there is the possibility that in the event that the low 4 o temperature switch malfunctions and does not open when the water has been heated electrically to above the predetermined temperature there could be a build up of excess pressure in the storage tank.

It has been found that it is possible to use an automatically re-setting type of switch in place of the button re-setting type provided that a io: latching solenoid activated switch is incorporated in the control circuit in :oo series between the over temperature switch and the electric heating element

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<A L& -H A 3 Thus the invention resides in a control circuit for an electrically boosted solar hot water unit wherein the supply of electric current to the heating element is controlled by a normally open thermally responsive low temperature switch which closes when the temperature of the water in the unit falls below a predetermined limit and an automatically resetting normally closed thermally responsive temperature switch which opens when the temperature of water in the unit exceeds a predetermine upper limit characterised in that a normally closed solenoid activated failsafe switch is positioned in series between the over temperature switch and the heating element, said solenoid being activated to open the fail-safe switch when current flows through a secondary circuit connected across the terminals of the over temperature switch.

The fail safe switch is designed for a once only operation so that it must be replaced or reset by a competent operator once the mal functioning component has been replaced or repaired.

The invention will be better understood by reference to the following description of the specific embodiments shown in the accompanying drawings wherein:ao o Fig.1. is a circuit diagram of one embodiment incorporating a 20 diagrammatic representation of a solenoid actuated fail safe switch which is 4*00.0 a capable of being reset; and Fig.2 is a similar circuit diagram showing a novel once only operation solenoid fail safe switch.

.f G ,As shown in the circuit diagram of Fig. 1 an electric boosting element 11 is 25 connected to an electric power supply through active line A and neutral oio o0+ ~line N. Incorporated in the active line in series is a thermally responsive low temperature switch 12 which is adapted to close when the temperature of the water in the solar hot water unit falls below a predetermined 4 lower limit, say 55 0 a thermally responsive over temperature switch (normally closed) and a normally closed solenoid latching switch 14. The coil winding of the solenoid switch 14 is connected across the terminals 13a and 13b of the over temperature switch 13, The end of the solenoid plunger 15, which projects beyond the housing 16 is provided with a groove 17. A spring loaded arm 18 bears against the side of the projecting portion of the plunger 15. The over temperature switch is adapted to open when the temperature of the water exceeds a predetermined upper limit say 95 0

C.

When the unit is in the electric heating mode and the temperature of the water falls below 55°C. the low temperature switch will close and current will follow the path of least resistance and flow through closed switch 12, the over temperature switch and the closed terminals of the fail-safe switch to the heating element 11 to heat the water. If the low temperature switch 12 mal-functions and fails to open when the temperature of the water reaches 55°C. the element 11 will continue to heat the water until the over temperature switch 13 opens. Current will then flow through the solenoid coil to cause the plunger 15 to retract and open the solenoid switch 14. When the plunger retracts the 20 arm 18 will engage in the groove 17 thus locking the solenoid switch in the open position. When the fault has been rectified the solenoid switch :may be reset by disengaging the arm 18 and allowing spring 19 to return the plunger 15 to its normally closed position.

o In the embodiment shown in Fig.2 of the drawings the circuit is essentially the same except that the resettable solenoid switch has been replaced by a novel once only operation solenoid 21. The plunger 22 of the solenoid is oY shortened so that it is totally enclosed within the solenoid housing 23. The switch is biassed to the closed position by a coil spring 24 positioned around the plunger between the inner end of a bobbin 25 on which the coil of the solenoid is wound and an annular disc 26 which bridges across the terminals 27 when the switch is in the closed position. The inner end 0 29 the inner end of which bears against the plunger 22. When the solenoid is activated the plunger moves to open the switch by disengaging the disc 26 from the terminals 27, the locking pin 29 engaging a groove 20 formed in the outer face of the plunger. This locks the switch in the open position and as the pin 29 is only accessible by destroying the housing the solenoid must be replaced before the hot water unit can be returned to service.

It will be obvious that in both the specific embodiments described above that when the the low temperature switch is functioning normaiy and the water has been heated to above 550c by solar radiation there Cal be no flow of electric current through the circuit and therefore the solenoid will not be activated even when the over temperature switch opens when the temperature exceeds the predetermined upper limit When the water cools below the pretermined, upper limit the over temperature switch will close but no current can flow whilst the low temperature switch remains open.

Claims

1. A CONTROL CIRCUIT for an electrically boosted solar hot water unit wherein the supply of electric current to the heating element is controlled by a normally open thermally responsive luw temperature switch which closes w-hen the temperature of the water in the unit falls below a predetermined limit and a normally closed thermally responsive over temperature switch which opens when the temperature of the water exceeds a predetermined upper limit characterised in that a normally closed solenoid activated fail-safe switch is positioned in series between the over temperature switch and the heating element, said solenoid being activated to open the fail-safe switch when current flows through a secondary circuit connected across the terminals of the over temperature switch.

2. A CONTROL CIRCUIT as claimed in claim 1 wherein the means for opening the fail-safe switch are capable of a once only operation.

3. A CONTROL CIRCUIT as claimed in claim 2 wherein the plunger of the solenoid switch is totally enclosed in a sealed housing and a spring loaded pin engages the plunger to lock it against further movement when it moves to the open position

4. A CONTROL CIRCUIT as claimed in claim 1 wherein the means for opening the fail-safe switch are resettable.

A CONTROL CIRCUIT as claimed in claim 4 wherein the fail-safe switch solenoid which is spring loaded to the closed position and when the 0 coil is activated moves the plunger to open the switch, the plunger is 6provided with a peripheral groove, and a spring loaded arm bears against the plunger to engage the groove and hold the plunger in the open position.

6. A CONTROL CIRCUIT for an electrically boosted solar hot water unit I t substantially as herein described with reference to Figs. 1 or 2 of the accompanying drawings. ALAN COLLIER EDWARDS APPLICANT 15th..June 1994 o- S S G i -V L~ t j