Electric heating – Heating devices – With protective means for heater
Patent
1997-09-02
1999-05-04
Paschall, Mark H.
Electric heating
Heating devices
With protective means for heater
219517, 219508, 219494, H05B 102
Patent
active
059001763
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a temperature sensitive protective device for solar hot water systems.
FIELD OF THE INVENTION
It is a requirement of the Australian Standards and other electrical safety codes that an electric hot water system be fitted with an electrical cut-out device (ECO) which safeguards against failure of the control thermostat.
Normally, the control thermostat senses the temperature of the water in the hot water system and makes an electric circuit to the heating element when the water temperature fills below the thermostat set point. When the water temperature rises to above the set point, the circuit is broken and the heating element is de-energised. The ECO is provided to protect the system in the event of the contact of the control thermostat becoming locked in the closed position. The ECO senses the water temperature and if it rises to 95.degree. C. or thereabouts failure of the control thermostat is inferred. The ECO then activates and breaks the electrical circuit to the heating element.
The codes require that the ECO be a device which does not automatically reset. It is a requirement that a technician manually reset the device in the event of activation. In the case of solar hot water systems, it is possible for the water to approach 95.degree. C. as a result of energy input by the solar collectors. Hence, it is desirable that the ECO distinguish between the water being heated by solar energy and electrical energy, otherwise the device will activate whenever the water temperature rises to about 95.degree. C. regardless of the cause of the temperature rise.
The present invention provides a means by which, in a solar water heater with an electric booster the ECO can distinguish between a rise in temperature brought about by electric means or by solar energy.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention there is provided a temperature sensitive protective device for a solar water heater comprising an electric booster characterized by a first and a second automatically resetting thermostat, a resilient means, an actuator, a first switch means and a second switch means and a fusible resistor, the first and second thermostats being in either a closed state or an open state and the first and second switch means being in either a closed state or an open state, wherein the first thermostat normally changes state at a first relatively low temperature and the second thermostat normally changes state at a second relatively high temperature, the fuisible resistor normally holding the resilient means in a compressed state, power for the electric booster being supplied via an electrical circuit through the second switch means, whereby if the first thermostat does not change state above the first temperature and the second thermostat then changes state, the electrical circuit supplying the electric booster is automatically disabled by the first stitch means being caused to change state, the fuisible resistor fusing and disintegrating thereby releasing the resident means, the released resilient means then urging the actuator so as to change the state of the second switch means and thus removing power to the electric booster.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic circuit diagram of a first embodiment of a temperature sensitive protective device in accordance with of the present invention; and
FIG. 2 is a sectional view of a temperature sensitive protective device incorporating the electric circuit of FIG. 1;
FIG. 3 is a schematic circuit diagram of a second embodiment of a temperature sensitive protective device in accordance with the present invention;
FIG. 4 is a sectional view of a temperature sensitive protective device incorporating the electrical circuit of FIG. 3; and
FIG. 5 is a sectional view of an alternative arrangement for use with the second embodiment of the present invention.
DESCRIPTION OF THE
Berrer Friedrich Edward
Tassicker Phillip Graham
Hardie Energy Products Pty Ltd
Paschall Mark H.
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